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 $178.85   4.142%   $186.258   $186.26   $186.25   $186.30  
  Purchase #2 $155.82   12.174%   $174.7895   $174.79   $174.80   $174.80  
  Purchase #3 $6.44   12.440%   $7.2411   $7.24   $7.25   $7.20  
  Purchase #4 $68.64   10.190%   $75.6344   $75.63   $75.65   $75.60  
  Purchase #5 $110.98   10.404%   $122.5264   $122.53   $122.55   $122.50  
  Purchase #6 $88.89   6.829%   $94.9603   $94.96   $94.95   $95.00  
  Purchase #7 $154.64   4.237%   $161.1921   $161.19   $161.20   $161.20  
  7 purchase totals = $764.26       $822.6018   $822.60   $822.65   $822.60