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 $102.32   10.464%   $113.0268   $113.03   $113.05   $113.00  
  Purchase #2 $9.58   10.603%   $10.5958   $10.60   $10.60   $10.60  
  Purchase #3 $151.36   13.521%   $171.8254   $171.83   $171.85   $171.80  
  Purchase #4 $155.56   7.330%   $166.9625   $166.96   $166.95   $167.00  
  Purchase #5 $123.30   11.373%   $137.3229   $137.32   $137.30   $137.30  
  Purchase #6 $206.76   3.398%   $213.7857   $213.79   $213.80   $213.80  
  Purchase #7 $17.86   5.288%   $18.8044   $18.80   $18.80   $18.80  
  7 purchase totals = $766.74       $832.3235   $832.33   $832.35   $832.30