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 $214.89   12.304%   $241.3301   $241.33   $241.35   $241.30  
  Purchase #2 $108.73   9.207%   $118.7408   $118.74   $118.75   $118.70  
  Purchase #3 $86.84   11.406%   $96.745   $96.75   $96.75   $96.70  
  Purchase #4 $247.26   11.836%   $276.5257   $276.53   $276.55   $276.50  
  Purchase #5 $229.34   8.533%   $248.9096   $248.91   $248.90   $248.90  
  Purchase #6 $21.91   4.166%   $22.8228   $22.82   $22.80   $22.80  
  Purchase #7 $230.59   5.528%   $243.337   $243.34   $243.35   $243.30  
  7 purchase totals = $1,139.56       $1,248.4110   $1,248.42   $1,248.45   $1,248.20