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 $22.53   11.573%   $25.1374   $25.14   $25.15   $25.10  
  Purchase #2 $180.73   13.593%   $205.2966   $205.30   $205.30   $205.30  
  Purchase #3 $157.61   3.843%   $163.667   $163.67   $163.65   $163.70  
  Purchase #4 $48.83   12.526%   $54.9464   $54.95   $54.95   $54.90  
  Purchase #5 $90.30   6.397%   $96.0765   $96.08   $96.10   $96.10  
  Purchase #6 $202.69   13.810%   $230.6815   $230.68   $230.70   $230.70  
  Purchase #7 $151.77   8.570%   $164.7767   $164.78   $164.80   $164.80  
  7 purchase totals = $854.46       $940.5821   $940.60   $940.65   $940.60