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 $84.95   11.318%   $94.5646   $94.56   $94.55   $94.60  
  Purchase #2 $58.35   7.499%   $62.7257   $62.73   $62.75   $62.70  
  Purchase #3 $161.99   12.252%   $181.837   $181.84   $181.85   $181.80  
  Purchase #4 $19.83   6.190%   $21.0575   $21.06   $21.05   $21.10  
  Purchase #5 $155.64   13.279%   $176.3074   $176.31   $176.30   $176.30  
  Purchase #6 $161.95   7.204%   $173.6169   $173.62   $173.60   $173.60  
  Purchase #7 $249.99   4.613%   $261.522   $261.52   $261.50   $261.50  
  7 purchase totals = $892.70       $971.6311   $971.64   $971.60   $971.60