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 $119.40   8.339%   $129.3568   $129.36   $129.35   $129.40  
  Purchase #2 $54.72   9.386%   $59.856   $59.86   $59.85   $59.90  
  Purchase #3 $99.83   8.811%   $108.626   $108.63   $108.65   $108.60  
  Purchase #4 $165.42   4.809%   $173.375   $173.38   $173.40   $173.40  
  Purchase #5 $99.57   7.483%   $107.0208   $107.02   $107.00   $107.00  
  Purchase #6 $221.31   10.513%   $244.5763   $244.58   $244.60   $244.60  
  Purchase #7 $187.42   11.795%   $209.5262   $209.53   $209.55   $209.50  
  7 purchase totals = $947.67       $1,032.3371   $1,032.36   $1,032.40   $1,032.40