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 $224.56   9.819%   $246.6095   $246.61   $246.60   $246.60  
  Purchase #2 $32.73   3.545%   $33.8903   $33.89   $33.90   $33.90  
  Purchase #3 $84.39   4.585%   $88.2593   $88.26   $88.25   $88.30  
  Purchase #4 $129.67   3.511%   $134.2227   $134.22   $134.20   $134.20  
  Purchase #5 $50.46   6.195%   $53.586   $53.59   $53.60   $53.60  
  Purchase #6 $128.52   5.377%   $135.4305   $135.43   $135.45   $135.40  
  Purchase #7 $103.68   12.404%   $116.5405   $116.54   $116.55   $116.50  
  7 purchase totals = $754.01       $808.5388   $808.54   $808.55   $808.50