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 $82.96   11.632%   $92.6099   $92.61   $92.60   $92.60  
  Purchase #2 $138.46   7.728%   $149.1602   $149.16   $149.15   $149.20  
  Purchase #3 $189.91   6.236%   $201.7528   $201.75   $201.75   $201.80  
  Purchase #4 $206.76   13.556%   $234.7884   $234.79   $234.80   $234.80  
  Purchase #5 $17.88   11.324%   $19.9047   $19.90   $19.90   $19.90  
  Purchase #6 $100.58   12.460%   $113.1123   $113.11   $113.10   $113.10  
  Purchase #7 $140.80   4.808%   $147.5697   $147.57   $147.55   $147.60  
  7 purchase totals = $877.35       $958.8980   $958.89   $958.85   $959.00