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 $203.97   12.831%   $230.1414   $230.14   $230.15   $230.10  
  Purchase #2 $49.72   8.300%   $53.8468   $53.85   $53.85   $53.80  
  Purchase #3 $221.74   11.302%   $246.8011   $246.80   $246.80   $246.80  
  Purchase #4 $43.36   11.381%   $48.2948   $48.29   $48.30   $48.30  
  Purchase #5 $209.35   13.362%   $237.3233   $237.32   $237.30   $237.30  
  Purchase #6 $119.79   5.279%   $126.1137   $126.11   $126.10   $126.10  
  Purchase #7 $214.67   7.769%   $231.3477   $231.35   $231.35   $231.30  
  7 purchase totals = $1,062.60       $1,173.8688   $1,173.86   $1,173.85   $1,173.70