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 $200.94   5.602%   $212.1967   $212.20   $212.20   $212.20  
  Purchase #2 $44.98   3.283%   $46.4567   $46.46   $46.45   $46.50  
  Purchase #3 $72.96   6.649%   $77.8111   $77.81   $77.80   $77.80  
  Purchase #4 $130.64   5.302%   $137.5665   $137.57   $137.55   $137.60  
  Purchase #5 $235.98   13.554%   $267.9647   $267.96   $267.95   $268.00  
  Purchase #6 $239.90   13.199%   $271.5644   $271.56   $271.55   $271.60  
  Purchase #7 $241.87   7.598%   $260.2473   $260.25   $260.25   $260.20  
  7 purchase totals = $1,167.27       $1,273.8074   $1,273.81   $1,273.75   $1,273.90