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 $246.94   12.561%   $277.9581   $277.96   $277.95   $278.00  
  Purchase #2 $42.43   4.395%   $44.2948   $44.29   $44.30   $44.30  
  Purchase #3 $8.85   4.543%   $9.2521   $9.25   $9.25   $9.30  
  Purchase #4 $160.48   8.644%   $174.3519   $174.35   $174.35   $174.40  
  Purchase #5 $199.46   10.141%   $219.6872   $219.69   $219.70   $219.70  
  Purchase #6 $158.85   5.669%   $167.8552   $167.86   $167.85   $167.90  
  Purchase #7 $115.69   11.655%   $129.1737   $129.17   $129.15   $129.20  
  7 purchase totals = $932.70       $1,022.5730   $1,022.57   $1,022.55   $1,022.80