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 $88.31   11.647%   $98.5955   $98.60   $98.60   $98.60  
  Purchase #2 $167.31   5.470%   $176.4619   $176.46   $176.45   $176.50  
  Purchase #3 $192.83   4.220%   $200.9674   $200.97   $200.95   $201.00  
  Purchase #4 $153.53   3.272%   $158.5535   $158.55   $158.55   $158.60  
  Purchase #5 $247.35   4.719%   $259.0224   $259.02   $259.00   $259.00  
  Purchase #6 $187.34   10.349%   $206.7278   $206.73   $206.75   $206.70  
  Purchase #7 $99.58   4.671%   $104.2314   $104.23   $104.25   $104.20  
  7 purchase totals = $1,136.25       $1,204.5599   $1,204.56   $1,204.55   $1,204.60