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 $235.73   6.506%   $251.0666   $251.07   $251.05   $251.10  
  Purchase #2 $138.95   7.711%   $149.6644   $149.66   $149.65   $149.70  
  Purchase #3 $34.70   13.645%   $39.4348   $39.43   $39.45   $39.40  
  Purchase #4 $142.94   13.254%   $161.8853   $161.89   $161.90   $161.90  
  Purchase #5 $94.36   8.461%   $102.3438   $102.34   $102.35   $102.30  
  Purchase #6 $245.38   11.804%   $274.3447   $274.34   $274.35   $274.30  
  Purchase #7 $80.39   5.642%   $84.9256   $84.93   $84.95   $84.90  
  7 purchase totals = $972.45       $1,063.6652   $1,063.66   $1,063.70   $1,063.60