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 $52.94   4.516%   $55.3308   $55.33   $55.35   $55.30  
  Purchase #2 $95.62   11.230%   $106.3581   $106.36   $106.35   $106.40  
  Purchase #3 $185.25   3.620%   $191.9561   $191.96   $191.95   $192.00  
  Purchase #4 $246.99   12.776%   $278.5454   $278.55   $278.55   $278.50  
  Purchase #5 $189.79   7.308%   $203.6599   $203.66   $203.65   $203.70  
  Purchase #6 $229.47   13.759%   $261.0428   $261.04   $261.05   $261.00  
  Purchase #7 $146.60   10.389%   $161.8303   $161.83   $161.85   $161.80  
  7 purchase totals = $1,146.66       $1,258.7234   $1,258.73   $1,258.75   $1,258.70