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 $249.35   13.155%   $282.152   $282.15   $282.15   $282.20  
  Purchase #2 $195.44   4.755%   $204.7332   $204.73   $204.75   $204.70  
  Purchase #3 $29.48   11.863%   $32.9772   $32.98   $33.00   $33.00  
  Purchase #4 $53.90   12.593%   $60.6876   $60.69   $60.70   $60.70  
  Purchase #5 $248.32   10.755%   $275.0268   $275.03   $275.05   $275.00  
  Purchase #6 $193.43   13.713%   $219.9551   $219.96   $219.95   $220.00  
  Purchase #7 $165.37   9.176%   $180.5444   $180.54   $180.55   $180.50  
  7 purchase totals = $1,135.29       $1,256.0763   $1,256.08   $1,256.15   $1,256.10