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 $184.38   5.629%   $194.7588   $194.76   $194.75   $194.80  
  Purchase #2 $241.58   4.776%   $253.1179   $253.12   $253.10   $253.10  
  Purchase #3 $96.32   10.463%   $106.398   $106.40   $106.40   $106.40  
  Purchase #4 $6.60   12.462%   $7.4225   $7.42   $7.40   $7.40  
  Purchase #5 $224.26   13.116%   $253.6739   $253.67   $253.65   $253.70  
  Purchase #6 $94.31   6.647%   $100.5788   $100.58   $100.60   $100.60  
  Purchase #7 $104.97   13.263%   $118.8922   $118.89   $118.90   $118.90  
  7 purchase totals = $952.42       $1,034.8421   $1,034.84   $1,034.80   $1,034.90