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 $249.62   5.253%   $262.7325   $262.73   $262.75   $262.70  
  Purchase #2 $23.66   10.730%   $26.1987   $26.20   $26.20   $26.20  
  Purchase #3 $34.62   6.102%   $36.7325   $36.73   $36.75   $36.70  
  Purchase #4 $132.29   3.543%   $136.977   $136.98   $137.00   $137.00  
  Purchase #5 $174.52   8.334%   $189.0645   $189.06   $189.05   $189.10  
  Purchase #6 $124.78   6.535%   $132.9344   $132.93   $132.95   $132.90  
  Purchase #7 $211.49   9.795%   $232.2054   $232.21   $232.20   $232.20  
  7 purchase totals = $950.98       $1,016.8450   $1,016.84   $1,016.90   $1,016.80