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 $24.67   7.649%   $26.557   $26.56   $26.55   $26.60  
  Purchase #2 $106.85   10.802%   $118.3919   $118.39   $118.40   $118.40  
  Purchase #3 $46.57   13.814%   $53.0032   $53.00   $53.00   $53.00  
  Purchase #4 $185.73   7.300%   $199.2883   $199.29   $199.30   $199.30  
  Purchase #5 $181.85   10.748%   $201.3952   $201.40   $201.40   $201.40  
  Purchase #6 $53.80   12.681%   $60.6224   $60.62   $60.60   $60.60  
  Purchase #7 $202.58   12.807%   $228.5244   $228.52   $228.50   $228.50  
  7 purchase totals = $802.05       $887.7824   $887.78   $887.75   $887.80