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 $22.85   11.702%   $25.5239   $25.52   $25.50   $25.50  
  Purchase #2 $119.88   5.295%   $126.2276   $126.23   $126.25   $126.20  
  Purchase #3 $59.77   9.403%   $65.3902   $65.39   $65.40   $65.40  
  Purchase #4 $178.44   9.248%   $194.9421   $194.94   $194.95   $194.90  
  Purchase #5 $207.80   12.407%   $233.5817   $233.58   $233.60   $233.60  
  Purchase #6 $225.62   5.449%   $237.914   $237.91   $237.90   $237.90  
  Purchase #7 $152.64   4.486%   $159.4874   $159.49   $159.50   $159.50  
  7 purchase totals = $967.00       $1,043.0669   $1,043.06   $1,043.10   $1,043.00