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 $82.91   12.199%   $93.0242   $93.02   $93.00   $93.00  
  Purchase #2 $180.67   10.806%   $200.1932   $200.19   $200.20   $200.20  
  Purchase #3 $210.77   13.213%   $238.619   $238.62   $238.60   $238.60  
  Purchase #4 $244.34   12.166%   $274.0664   $274.07   $274.05   $274.10  
  Purchase #5 $199.33   11.858%   $222.9666   $222.97   $222.95   $223.00  
  Purchase #6 $148.65   3.562%   $153.9449   $153.94   $153.95   $153.90  
  Purchase #7 $12.57   7.657%   $13.5325   $13.53   $13.55   $13.50  
  7 purchase totals = $1,079.24       $1,196.3468   $1,196.34   $1,196.30   $1,196.30