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 $243.99   10.483%   $269.5675   $269.57   $269.55   $269.60  
  Purchase #2 $98.66   12.426%   $110.9195   $110.92   $110.90   $110.90  
  Purchase #3 $87.60   4.747%   $91.7584   $91.76   $91.75   $91.80  
  Purchase #4 $243.31   10.440%   $268.7116   $268.71   $268.70   $268.70  
  Purchase #5 $232.82   11.324%   $259.1845   $259.18   $259.20   $259.20  
  Purchase #6 $181.30   13.738%   $206.207   $206.21   $206.20   $206.20  
  Purchase #7 $51.51   13.544%   $58.4865   $58.49   $58.50   $58.50  
  7 purchase totals = $1,139.19       $1,264.8350   $1,264.84   $1,264.80   $1,264.90