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 $38.93   6.843%   $41.594   $41.59   $41.60   $41.60  
  Purchase #2 $228.78   10.542%   $252.898   $252.90   $252.90   $252.90  
  Purchase #3 $219.58   6.551%   $233.9647   $233.96   $233.95   $234.00  
  Purchase #4 $113.73   7.756%   $122.5509   $122.55   $122.55   $122.60  
  Purchase #5 $112.56   3.176%   $116.1349   $116.13   $116.15   $116.10  
  Purchase #6 $22.82   9.158%   $24.9099   $24.91   $24.90   $24.90  
  Purchase #7 $5.58   10.378%   $6.1591   $6.16   $6.15   $6.20  
  7 purchase totals = $741.98       $798.2115   $798.20   $798.20   $798.30