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 $119.25   5.822%   $126.1927   $126.19   $126.20   $126.20  
  Purchase #2 $123.59   4.767%   $129.4815   $129.48   $129.50   $129.50  
  Purchase #3 $66.97   13.713%   $76.1536   $76.15   $76.15   $76.20  
  Purchase #4 $201.95   12.207%   $226.602   $226.60   $226.60   $226.60  
  Purchase #5 $175.74   4.362%   $183.4058   $183.41   $183.40   $183.40  
  Purchase #6 $236.98   3.379%   $244.9876   $244.99   $245.00   $245.00  
  Purchase #7 $51.55   8.571%   $55.9684   $55.97   $55.95   $56.00  
  7 purchase totals = $976.03       $1,042.7916   $1,042.79   $1,042.80   $1,042.90