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 $185.46   10.714%   $205.3302   $205.33   $205.35   $205.30  
  Purchase #2 $245.53   7.519%   $263.9914   $263.99   $264.00   $264.00  
  Purchase #3 $220.47   11.259%   $245.2927   $245.29   $245.30   $245.30  
  Purchase #4 $84.41   8.258%   $91.3806   $91.38   $91.40   $91.40  
  Purchase #5 $197.79   8.415%   $214.434   $214.43   $214.45   $214.40  
  Purchase #6 $231.99   8.181%   $250.9691   $250.97   $250.95   $251.00  
  Purchase #7 $228.27   3.691%   $236.6954   $236.70   $236.70   $236.70  
  7 purchase totals = $1,393.92       $1,508.0934   $1,508.09   $1,508.15   $1,508.10