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 $23.52   9.275%   $25.7015   $25.70   $25.70   $25.70  
  Purchase #2 $232.55   10.143%   $256.1375   $256.14   $256.15   $256.10  
  Purchase #3 $195.37   10.560%   $216.0011   $216.00   $216.00   $216.00  
  Purchase #4 $161.41   11.594%   $180.1239   $180.12   $180.10   $180.10  
  Purchase #5 $44.26   8.118%   $47.853   $47.85   $47.85   $47.90  
  Purchase #6 $205.95   5.566%   $217.4132   $217.41   $217.40   $217.40  
  Purchase #7 $174.61   3.276%   $180.3302   $180.33   $180.35   $180.30  
  7 purchase totals = $1,037.67       $1,123.5604   $1,123.55   $1,123.55   $1,123.50