Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $141.48   12.172%   $158.7009   $158.70   $158.70   $158.70  
  Purchase #2 $204.64   10.378%   $225.8775   $225.88   $225.90   $225.90  
  Purchase #3 $183.45   12.264%   $205.9483   $205.95   $205.95   $205.90  
  Purchase #4 $241.99   13.829%   $275.4548   $275.45   $275.45   $275.50  
  Purchase #5 $12.70   13.288%   $14.3876   $14.39   $14.40   $14.40  
  Purchase #6 $247.83   13.791%   $282.0082   $282.01   $282.00   $282.00  
  Purchase #7 $156.77   9.565%   $171.7651   $171.77   $171.75   $171.80  
  7 purchase totals = $1,188.86       $1,334.1424   $1,334.15   $1,334.15   $1,334.20