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 $156.38   8.248%   $169.2782   $169.28   $169.30   $169.30  
  Purchase #2 $245.82   5.346%   $258.9615   $258.96   $258.95   $259.00  
  Purchase #3 $185.50   9.221%   $202.605   $202.61   $202.60   $202.60  
  Purchase #4 $43.98   7.466%   $47.2635   $47.26   $47.25   $47.30  
  Purchase #5 $25.37   10.757%   $28.0991   $28.10   $28.10   $28.10  
  Purchase #6 $243.78   4.183%   $253.9773   $253.98   $254.00   $254.00  
  Purchase #7 $94.89   3.437%   $98.1514   $98.15   $98.15   $98.20  
  7 purchase totals = $995.72       $1,058.3360   $1,058.34   $1,058.35   $1,058.50