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 $34.49   8.596%   $37.4548   $37.45   $37.45   $37.50  
  Purchase #2 $90.91   4.442%   $94.9482   $94.95   $94.95   $94.90  
  Purchase #3 $235.65   5.761%   $249.2258   $249.23   $249.25   $249.20  
  Purchase #4 $106.67   9.330%   $116.6223   $116.62   $116.60   $116.60  
  Purchase #5 $206.69   12.696%   $232.9314   $232.93   $232.95   $232.90  
  Purchase #6 $169.29   8.194%   $183.1616   $183.16   $183.15   $183.20  
  Purchase #7 $113.78   3.731%   $118.0251   $118.03   $118.05   $118.00  
  7 purchase totals = $957.48       $1,032.3692   $1,032.37   $1,032.40   $1,032.30