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 $187.58   6.573%   $199.9096   $199.91   $199.90   $199.90  
  Purchase #2 $166.57   10.872%   $184.6795   $184.68   $184.70   $184.70  
  Purchase #3 $58.73   6.765%   $62.7031   $62.70   $62.70   $62.70  
  Purchase #4 $31.71   12.591%   $35.7026   $35.70   $35.70   $35.70  
  Purchase #5 $171.80   11.559%   $191.6584   $191.66   $191.65   $191.70  
  Purchase #6 $26.62   13.816%   $30.2978   $30.30   $30.30   $30.30  
  Purchase #7 $182.83   4.369%   $190.8178   $190.82   $190.80   $190.80  
  7 purchase totals = $825.84       $895.7688   $895.77   $895.75   $895.80