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 $244.66   10.238%   $269.7083   $269.71   $269.70   $269.70  
  Purchase #2 $101.84   4.278%   $106.1967   $106.20   $106.20   $106.20  
  Purchase #3 $96.98   13.583%   $110.1528   $110.15   $110.15   $110.20  
  Purchase #4 $127.35   11.240%   $141.6641   $141.66   $141.65   $141.70  
  Purchase #5 $121.48   6.749%   $129.6787   $129.68   $129.70   $129.70  
  Purchase #6 $121.62   13.784%   $138.3841   $138.38   $138.40   $138.40  
  Purchase #7 $131.68   12.181%   $147.7199   $147.72   $147.70   $147.70  
  7 purchase totals = $945.61       $1,043.5046   $1,043.50   $1,043.50   $1,043.60