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 $94.51   12.622%   $106.4391   $106.44   $106.45   $106.40  
  Purchase #2 $132.28   13.789%   $150.5201   $150.52   $150.50   $150.50  
  Purchase #3 $158.49   7.725%   $170.7334   $170.73   $170.75   $170.70  
  Purchase #4 $195.74   4.749%   $205.0357   $205.04   $205.05   $205.00  
  Purchase #5 $214.84   12.628%   $241.97   $241.97   $241.95   $242.00  
  Purchase #6 $39.92   10.209%   $43.9954   $44.00   $44.00   $44.00  
  Purchase #7 $134.54   11.308%   $149.7538   $149.75   $149.75   $149.80  
  7 purchase totals = $970.32       $1,068.4475   $1,068.45   $1,068.45   $1,068.40