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 $54.86   13.838%   $62.4515   $62.45   $62.45   $62.50  
  Purchase #2 $235.56   10.663%   $260.6778   $260.68   $260.70   $260.70  
  Purchase #3 $67.52   13.158%   $76.4043   $76.40   $76.40   $76.40  
  Purchase #4 $84.94   4.721%   $88.95   $88.95   $88.95   $89.00  
  Purchase #5 $136.64   12.542%   $153.7774   $153.78   $153.80   $153.80  
  Purchase #6 $107.85   4.221%   $112.4023   $112.40   $112.40   $112.40  
  Purchase #7 $74.31   7.762%   $80.0779   $80.08   $80.10   $80.10  
  7 purchase totals = $761.68       $834.7412   $834.74   $834.80   $834.90