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 $33.41   11.726%   $37.3277   $37.33   $37.35   $37.30  
  Purchase #2 $206.88   13.378%   $234.5564   $234.56   $234.55   $234.60  
  Purchase #3 $227.36   7.844%   $245.1941   $245.19   $245.20   $245.20  
  Purchase #4 $82.29   5.554%   $86.8604   $86.86   $86.85   $86.90  
  Purchase #5 $172.91   12.643%   $194.771   $194.77   $194.75   $194.80  
  Purchase #6 $198.76   10.322%   $219.276   $219.28   $219.30   $219.30  
  Purchase #7 $86.48   11.196%   $96.1623   $96.16   $96.15   $96.20  
  7 purchase totals = $1,008.09       $1,114.1479   $1,114.15   $1,114.15   $1,114.30