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 $33.93   6.263%   $36.055   $36.06   $36.05   $36.10  
  Purchase #2 $177.73   9.578%   $194.753   $194.75   $194.75   $194.80  
  Purchase #3 $203.83   7.422%   $218.9583   $218.96   $218.95   $219.00  
  Purchase #4 $149.93   5.222%   $157.7593   $157.76   $157.75   $157.80  
  Purchase #5 $27.65   3.569%   $28.6368   $28.64   $28.65   $28.60  
  Purchase #6 $178.76   9.175%   $195.1612   $195.16   $195.15   $195.20  
  Purchase #7 $122.97   13.424%   $139.4775   $139.48   $139.50   $139.50  
  7 purchase totals = $894.80       $970.8011   $970.81   $970.80   $971.00