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 $201.49   7.206%   $216.0094   $216.01   $216.00   $216.00  
  Purchase #2 $146.64   12.431%   $164.8688   $164.87   $164.85   $164.90  
  Purchase #3 $233.82   4.697%   $244.8025   $244.80   $244.80   $244.80  
  Purchase #4 $235.88   9.596%   $258.515   $258.52   $258.50   $258.50  
  Purchase #5 $74.97   3.180%   $77.354   $77.35   $77.35   $77.40  
  Purchase #6 $55.85   3.625%   $57.8746   $57.87   $57.85   $57.90  
  Purchase #7 $7.41   4.103%   $7.714   $7.71   $7.70   $7.70  
  7 purchase totals = $956.06       $1,027.1383   $1,027.13   $1,027.05   $1,027.20