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 $183.29   6.699%   $195.5686   $195.57   $195.55   $195.60  
  Purchase #2 $85.80   6.328%   $91.2294   $91.23   $91.25   $91.20  
  Purchase #3 $97.29   5.576%   $102.7149   $102.71   $102.70   $102.70  
  Purchase #4 $242.60   7.394%   $260.5378   $260.54   $260.55   $260.50  
  Purchase #5 $175.78   10.651%   $194.5023   $194.50   $194.50   $194.50  
  Purchase #6 $83.40   7.578%   $89.7201   $89.72   $89.70   $89.70  
  Purchase #7 $84.99   3.556%   $88.0122   $88.01   $88.00   $88.00  
  7 purchase totals = $953.15       $1,022.2853   $1,022.28   $1,022.25   $1,022.20