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 $234.40   11.547%   $261.4662   $261.47   $261.45   $261.50  
  Purchase #2 $201.73   3.460%   $208.7099   $208.71   $208.70   $208.70  
  Purchase #3 $154.52   12.319%   $173.5553   $173.56   $173.55   $173.60  
  Purchase #4 $39.84   11.511%   $44.426   $44.43   $44.45   $44.40  
  Purchase #5 $25.51   13.298%   $28.9023   $28.90   $28.90   $28.90  
  Purchase #6 $10.51   13.109%   $11.8878   $11.89   $11.90   $11.90  
  Purchase #7 $232.95   6.742%   $248.6555   $248.66   $248.65   $248.70  
  7 purchase totals = $899.46       $977.6030   $977.62   $977.60   $977.70