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 $230.36   6.771%   $245.9577   $245.96   $245.95   $246.00  
  Purchase #2 $177.67   11.632%   $198.3366   $198.34   $198.35   $198.30  
  Purchase #3 $73.99   3.622%   $76.6699   $76.67   $76.65   $76.70  
  Purchase #4 $79.79   10.525%   $88.1879   $88.19   $88.20   $88.20  
  Purchase #5 $31.84   7.753%   $34.3086   $34.31   $34.30   $34.30  
  Purchase #6 $166.83   9.811%   $183.1977   $183.20   $183.20   $183.20  
  Purchase #7 $197.32   8.602%   $214.2935   $214.29   $214.30   $214.30  
  7 purchase totals = $957.80       $1,040.9519   $1,040.96   $1,040.95   $1,041.00