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 $92.33   6.669%   $98.4875   $98.49   $98.50   $98.50  
  Purchase #2 $235.38   4.203%   $245.273   $245.27   $245.25   $245.30  
  Purchase #3 $60.34   5.762%   $63.8168   $63.82   $63.80   $63.80  
  Purchase #4 $58.64   9.666%   $64.3081   $64.31   $64.30   $64.30  
  Purchase #5 $228.72   7.332%   $245.4898   $245.49   $245.50   $245.50  
  Purchase #6 $15.46   13.416%   $17.5341   $17.53   $17.55   $17.50  
  Purchase #7 $114.98   7.387%   $123.4736   $123.47   $123.45   $123.50  
  7 purchase totals = $805.85       $858.3829   $858.38   $858.35   $858.40