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 $234.32   9.324%   $256.168   $256.17   $256.15   $256.20  
  Purchase #2 $90.52   4.685%   $94.7609   $94.76   $94.75   $94.80  
  Purchase #3 $64.83   5.168%   $68.1804   $68.18   $68.20   $68.20  
  Purchase #4 $112.31   11.409%   $125.1234   $125.12   $125.10   $125.10  
  Purchase #5 $154.55   11.415%   $172.1919   $172.19   $172.20   $172.20  
  Purchase #6 $118.35   13.557%   $134.3947   $134.39   $134.40   $134.40  
  Purchase #7 $185.75   8.686%   $201.8842   $201.88   $201.90   $201.90  
  7 purchase totals = $960.63       $1,052.7035   $1,052.69   $1,052.70   $1,052.80