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 $144.67   4.618%   $151.3509   $151.35   $151.35   $151.40  
  Purchase #2 $199.26   6.813%   $212.8356   $212.84   $212.85   $212.80  
  Purchase #3 $11.36   3.659%   $11.7757   $11.78   $11.80   $11.80  
  Purchase #4 $99.61   7.836%   $107.4154   $107.42   $107.40   $107.40  
  Purchase #5 $93.76   9.661%   $102.8182   $102.82   $102.80   $102.80  
  Purchase #6 $34.71   3.646%   $35.9755   $35.98   $36.00   $36.00  
  Purchase #7 $194.45   3.189%   $200.651   $200.65   $200.65   $200.70  
  7 purchase totals = $777.82       $822.8223   $822.84   $822.85   $822.90