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 $202.63   7.221%   $217.2619   $217.26   $217.25   $217.30  
  Purchase #2 $110.47   4.306%   $115.2268   $115.23   $115.25   $115.20  
  Purchase #3 $122.42   3.542%   $126.7561   $126.76   $126.75   $126.80  
  Purchase #4 $191.46   5.283%   $201.5748   $201.57   $201.55   $201.60  
  Purchase #5 $85.73   5.587%   $90.5197   $90.52   $90.50   $90.50  
  Purchase #6 $83.83   5.488%   $88.4306   $88.43   $88.45   $88.40  
  Purchase #7 $154.75   8.783%   $168.3417   $168.34   $168.35   $168.30  
  7 purchase totals = $951.29       $1,008.1116   $1,008.11   $1,008.10   $1,008.10