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 $202.43   3.217%   $208.9422   $208.94   $208.95   $208.90  
  Purchase #2 $212.95   9.390%   $232.946   $232.95   $232.95   $232.90  
  Purchase #3 $114.34   4.487%   $119.4704   $119.47   $119.45   $119.50  
  Purchase #4 $146.45   11.574%   $163.4001   $163.40   $163.40   $163.40  
  Purchase #5 $195.47   3.700%   $202.7024   $202.70   $202.70   $202.70  
  Purchase #6 $188.52   8.433%   $204.4179   $204.42   $204.40   $204.40  
  Purchase #7 $28.49   11.822%   $31.8581   $31.86   $31.85   $31.90  
  7 purchase totals = $1,088.65       $1,163.7371   $1,163.74   $1,163.70   $1,163.70