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 $82.72   7.127%   $88.6155   $88.62   $88.60   $88.60  
  Purchase #2 $87.29   8.786%   $94.9593   $94.96   $94.95   $95.00  
  Purchase #3 $198.26   6.378%   $210.905   $210.91   $210.90   $210.90  
  Purchase #4 $17.58   11.716%   $19.6397   $19.64   $19.65   $19.60  
  Purchase #5 $154.31   12.116%   $173.0062   $173.01   $173.00   $173.00  
  Purchase #6 $58.61   6.691%   $62.5316   $62.53   $62.55   $62.50  
  Purchase #7 $128.64   5.803%   $136.105   $136.11   $136.10   $136.10  
  7 purchase totals = $727.41       $785.7623   $785.78   $785.75   $785.70