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 $96.74   8.804%   $105.257   $105.26   $105.25   $105.30  
  Purchase #2 $102.94   9.823%   $113.0518   $113.05   $113.05   $113.10  
  Purchase #3 $104.80   6.774%   $111.8992   $111.90   $111.90   $111.90  
  Purchase #4 $22.80   11.170%   $25.3468   $25.35   $25.35   $25.30  
  Purchase #5 $55.37   12.646%   $62.3721   $62.37   $62.35   $62.40  
  Purchase #6 $250.97   12.792%   $283.0741   $283.07   $283.05   $283.10  
  Purchase #7 $50.47   9.299%   $55.1632   $55.16   $55.15   $55.20  
  7 purchase totals = $684.09       $756.1642   $756.16   $756.10   $756.30