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 $247.51   11.169%   $275.1544   $275.15   $275.15   $275.20  
  Purchase #2 $126.87   6.244%   $134.7918   $134.79   $134.80   $134.80  
  Purchase #3 $247.81   8.647%   $269.2381   $269.24   $269.25   $269.20  
  Purchase #4 $11.25   5.350%   $11.8519   $11.85   $11.85   $11.90  
  Purchase #5 $38.43   7.663%   $41.3749   $41.37   $41.35   $41.40  
  Purchase #6 $195.67   6.244%   $207.8876   $207.89   $207.90   $207.90  
  Purchase #7 $75.77   10.803%   $83.9554   $83.96   $83.95   $84.00  
  7 purchase totals = $943.31       $1,024.2541   $1,024.25   $1,024.25   $1,024.40