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 $97.78   6.459%   $104.0956   $104.10   $104.10   $104.10  
  Purchase #2 $44.82   10.131%   $49.3607   $49.36   $49.35   $49.40  
  Purchase #3 $118.84   11.350%   $132.3283   $132.33   $132.35   $132.30  
  Purchase #4 $182.73   8.522%   $198.3023   $198.30   $198.30   $198.30  
  Purchase #5 $95.92   9.334%   $104.8732   $104.87   $104.85   $104.90  
  Purchase #6 $210.39   5.419%   $221.791   $221.79   $221.80   $221.80  
  Purchase #7 $204.79   5.841%   $216.7518   $216.75   $216.75   $216.80  
  7 purchase totals = $955.27       $1,027.5029   $1,027.50   $1,027.50   $1,027.60