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 $245.87   11.242%   $273.5107   $273.51   $273.50   $273.50  
  Purchase #2 $124.89   3.422%   $129.1637   $129.16   $129.15   $129.20  
  Purchase #3 $180.94   11.790%   $202.2728   $202.27   $202.25   $202.30  
  Purchase #4 $25.39   4.667%   $26.575   $26.58   $26.60   $26.60  
  Purchase #5 $177.35   13.353%   $201.0315   $201.03   $201.05   $201.00  
  Purchase #6 $33.93   9.130%   $37.0278   $37.03   $37.05   $37.00  
  Purchase #7 $77.65   4.616%   $81.2343   $81.23   $81.25   $81.20  
  7 purchase totals = $866.02       $950.8158   $950.81   $950.85   $950.80