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 $236.43   11.817%   $264.3689   $264.37   $264.35   $264.40  
  Purchase #2 $166.82   5.519%   $176.0268   $176.03   $176.05   $176.00  
  Purchase #3 $157.89   10.698%   $174.7811   $174.78   $174.80   $174.80  
  Purchase #4 $209.68   7.720%   $225.8673   $225.87   $225.85   $225.90  
  Purchase #5 $156.25   13.154%   $176.8031   $176.80   $176.80   $176.80  
  Purchase #6 $223.60   10.468%   $247.0064   $247.01   $247.00   $247.00  
  Purchase #7 $209.88   4.545%   $219.419   $219.42   $219.40   $219.40  
  7 purchase totals = $1,360.55       $1,484.2726   $1,484.28   $1,484.25   $1,484.30