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 $232.82   13.541%   $264.3462   $264.35   $264.35   $264.30  
  Purchase #2 $151.94   9.708%   $166.6903   $166.69   $166.70   $166.70  
  Purchase #3 $222.70   9.808%   $244.5424   $244.54   $244.55   $244.50  
  Purchase #4 $25.59   3.721%   $26.5422   $26.54   $26.55   $26.50  
  Purchase #5 $156.49   4.493%   $163.5211   $163.52   $163.50   $163.50  
  Purchase #6 $229.73   12.595%   $258.6645   $258.66   $258.65   $258.70  
  Purchase #7 $60.85   5.391%   $64.1304   $64.13   $64.15   $64.10  
  7 purchase totals = $1,080.12       $1,188.4371   $1,188.43   $1,188.45   $1,188.30