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 $54.99   12.207%   $61.7026   $61.70   $61.70   $61.70  
  Purchase #2 $232.59   5.140%   $244.5451   $244.55   $244.55   $244.50  
  Purchase #3 $138.90   4.710%   $145.4422   $145.44   $145.45   $145.40  
  Purchase #4 $209.86   10.855%   $232.6403   $232.64   $232.65   $232.60  
  Purchase #5 $203.82   6.128%   $216.3101   $216.31   $216.30   $216.30  
  Purchase #6 $168.46   12.209%   $189.0273   $189.03   $189.05   $189.00  
  Purchase #7 $119.40   13.692%   $135.7482   $135.75   $135.75   $135.70  
  7 purchase totals = $1,128.02       $1,225.4158   $1,225.42   $1,225.45   $1,225.20