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 $107.72   10.161%   $118.6654   $118.67   $118.65   $118.70  
  Purchase #2 $226.89   6.499%   $241.6356   $241.64   $241.65   $241.60  
  Purchase #3 $206.68   6.625%   $220.3726   $220.37   $220.35   $220.40  
  Purchase #4 $246.56   6.802%   $263.331   $263.33   $263.35   $263.30  
  Purchase #5 $53.89   9.383%   $58.9465   $58.95   $58.95   $58.90  
  Purchase #6 $52.88   12.752%   $59.6233   $59.62   $59.60   $59.60  
  Purchase #7 $170.50   11.261%   $189.7   $189.70   $189.70   $189.70  
  7 purchase totals = $1,065.12       $1,152.2744   $1,152.28   $1,152.25   $1,152.20