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 $248.87   11.105%   $276.507   $276.51   $276.50   $276.50  
  Purchase #2 $244.77   13.549%   $277.9339   $277.93   $277.95   $277.90  
  Purchase #3 $60.92   5.754%   $64.4253   $64.43   $64.45   $64.40  
  Purchase #4 $51.56   7.336%   $55.3424   $55.34   $55.35   $55.30  
  Purchase #5 $131.48   9.220%   $143.6025   $143.60   $143.60   $143.60  
  Purchase #6 $5.52   7.840%   $5.9528   $5.95   $5.95   $6.00  
  Purchase #7 $194.27   4.621%   $203.2472   $203.25   $203.25   $203.20  
  7 purchase totals = $937.39       $1,027.0111   $1,027.01   $1,027.05   $1,026.90