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 $227.95   8.441%   $247.1913   $247.19   $247.20   $247.20  
  Purchase #2 $211.55   12.433%   $237.852   $237.85   $237.85   $237.90  
  Purchase #3 $70.38   9.532%   $77.0886   $77.09   $77.10   $77.10  
  Purchase #4 $111.27   5.853%   $117.7826   $117.78   $117.80   $117.80  
  Purchase #5 $147.33   6.791%   $157.3352   $157.34   $157.35   $157.30  
  Purchase #6 $201.80   10.159%   $222.3009   $222.30   $222.30   $222.30  
  Purchase #7 $55.99   13.276%   $63.4232   $63.42   $63.40   $63.40  
  7 purchase totals = $1,026.27       $1,122.9738   $1,122.97   $1,123.00   $1,123.00