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 $209.26   8.874%   $227.8297   $227.83   $227.85   $227.80  
  Purchase #2 $226.57   4.307%   $236.3284   $236.33   $236.35   $236.30  
  Purchase #3 $21.51   5.405%   $22.6726   $22.67   $22.65   $22.70  
  Purchase #4 $176.44   12.517%   $198.525   $198.53   $198.55   $198.50  
  Purchase #5 $139.65   9.580%   $153.0285   $153.03   $153.05   $153.00  
  Purchase #6 $83.77   4.809%   $87.7985   $87.80   $87.80   $87.80  
  Purchase #7 $16.37   9.584%   $17.9389   $17.94   $17.95   $17.90  
  7 purchase totals = $873.57       $944.1216   $944.13   $944.20   $944.00