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 $175.37   5.220%   $184.5243   $184.52   $184.50   $184.50  
  Purchase #2 $70.61   3.702%   $73.224   $73.22   $73.20   $73.20  
  Purchase #3 $71.45   10.456%   $78.9208   $78.92   $78.90   $78.90  
  Purchase #4 $114.98   3.606%   $119.1262   $119.13   $119.15   $119.10  
  Purchase #5 $153.44   5.222%   $161.4526   $161.45   $161.45   $161.50  
  Purchase #6 $98.46   3.563%   $101.9681   $101.97   $101.95   $102.00  
  Purchase #7 $79.98   7.197%   $85.7362   $85.74   $85.75   $85.70  
  7 purchase totals = $764.29       $804.9522   $804.95   $804.90   $804.90