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 $46.81   12.424%   $52.6257   $52.63   $52.65   $52.60  
  Purchase #2 $174.65   11.171%   $194.1602   $194.16   $194.15   $194.20  
  Purchase #3 $228.50   6.860%   $244.1751   $244.18   $244.20   $244.20  
  Purchase #4 $10.51   4.388%   $10.9712   $10.97   $10.95   $11.00  
  Purchase #5 $49.42   8.622%   $53.681   $53.68   $53.70   $53.70  
  Purchase #6 $73.54   9.447%   $80.4873   $80.49   $80.50   $80.50  
  Purchase #7 $170.73   13.649%   $194.0329   $194.03   $194.05   $194.00  
  7 purchase totals = $754.16       $830.1334   $830.14   $830.20   $830.20