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 $33.40   9.699%   $36.6395   $36.64   $36.65   $36.60  
  Purchase #2 $210.87   7.588%   $226.8708   $226.87   $226.85   $226.90  
  Purchase #3 $203.93   13.479%   $231.4177   $231.42   $231.40   $231.40  
  Purchase #4 $126.93   3.578%   $131.4716   $131.47   $131.45   $131.50  
  Purchase #5 $108.28   13.118%   $122.4842   $122.48   $122.50   $122.50  
  Purchase #6 $240.43   10.781%   $266.3508   $266.35   $266.35   $266.40  
  Purchase #7 $217.74   5.591%   $229.9138   $229.91   $229.90   $229.90  
  7 purchase totals = $1,141.58       $1,245.1484   $1,245.14   $1,245.10   $1,245.20