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 $212.69   11.113%   $236.3262   $236.33   $236.35   $236.30  
  Purchase #2 $138.55   11.634%   $154.6689   $154.67   $154.65   $154.70  
  Purchase #3 $106.32   11.709%   $118.769   $118.77   $118.75   $118.80  
  Purchase #4 $64.78   5.804%   $68.5398   $68.54   $68.55   $68.50  
  Purchase #5 $129.93   5.208%   $136.6968   $136.70   $136.70   $136.70  
  Purchase #6 $141.91   9.623%   $155.566   $155.57   $155.55   $155.60  
  Purchase #7 $34.74   5.751%   $36.7379   $36.74   $36.75   $36.70  
  7 purchase totals = $828.92       $907.3046   $907.32   $907.30   $907.30