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 $232.53   7.610%   $250.2255   $250.23   $250.25   $250.20  
  Purchase #2 $124.37   6.263%   $132.1593   $132.16   $132.15   $132.20  
  Purchase #3 $147.89   12.537%   $166.431   $166.43   $166.45   $166.40  
  Purchase #4 $80.84   10.595%   $89.405   $89.41   $89.40   $89.40  
  Purchase #5 $56.81   10.308%   $62.666   $62.67   $62.65   $62.70  
  Purchase #6 $21.73   10.446%   $23.9999   $24.00   $24.00   $24.00  
  Purchase #7 $197.44   6.407%   $210.09   $210.09   $210.10   $210.10  
  7 purchase totals = $861.61       $934.9767   $934.99   $935.00   $935.00