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 $136.66   11.566%   $152.4661   $152.47   $152.45   $152.50  
  Purchase #2 $249.78   9.179%   $272.7073   $272.71   $272.70   $272.70  
  Purchase #3 $77.43   8.174%   $83.7591   $83.76   $83.75   $83.80  
  Purchase #4 $86.50   7.330%   $92.8405   $92.84   $92.85   $92.80  
  Purchase #5 $97.26   10.316%   $107.2933   $107.29   $107.30   $107.30  
  Purchase #6 $41.80   4.818%   $43.8139   $43.81   $43.80   $43.80  
  Purchase #7 $247.31   10.805%   $274.0318   $274.03   $274.05   $274.00  
  7 purchase totals = $936.74       $1,026.9120   $1,026.91   $1,026.90   $1,026.90