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 $234.58   13.171%   $265.4765   $265.48   $265.50   $265.50  
  Purchase #2 $66.79   10.319%   $73.6821   $73.68   $73.70   $73.70  
  Purchase #3 $238.46   13.140%   $269.7936   $269.79   $269.80   $269.80  
  Purchase #4 $120.66   4.241%   $125.7772   $125.78   $125.80   $125.80  
  Purchase #5 $23.39   5.366%   $24.6451   $24.65   $24.65   $24.60  
  Purchase #6 $153.70   5.288%   $161.8277   $161.83   $161.85   $161.80  
  Purchase #7 $33.34   12.160%   $37.3941   $37.39   $37.40   $37.40  
  7 purchase totals = $870.92       $958.5963   $958.60   $958.70   $958.60