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 $244.42   5.822%   $258.6501   $258.65   $258.65   $258.70  
  Purchase #2 $102.63   8.558%   $111.4131   $111.41   $111.40   $111.40  
  Purchase #3 $67.43   10.199%   $74.3072   $74.31   $74.30   $74.30  
  Purchase #4 $185.36   11.439%   $206.5633   $206.56   $206.55   $206.60  
  Purchase #5 $243.42   8.571%   $264.2835   $264.28   $264.30   $264.30  
  Purchase #6 $28.31   3.514%   $29.3048   $29.30   $29.30   $29.30  
  Purchase #7 $102.38   5.723%   $108.2392   $108.24   $108.25   $108.20  
  7 purchase totals = $973.95       $1,052.7612   $1,052.75   $1,052.75   $1,052.80