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 $17.52   10.492%   $19.3582   $19.36   $19.35   $19.40  
  Purchase #2 $195.57   7.829%   $210.8812   $210.88   $210.90   $210.90  
  Purchase #3 $129.68   9.783%   $142.3666   $142.37   $142.35   $142.40  
  Purchase #4 $70.37   5.763%   $74.4254   $74.43   $74.45   $74.40  
  Purchase #5 $219.95   3.235%   $227.0654   $227.07   $227.05   $227.10  
  Purchase #6 $177.54   3.803%   $184.2918   $184.29   $184.30   $184.30  
  Purchase #7 $139.80   13.356%   $158.4717   $158.47   $158.45   $158.50  
  7 purchase totals = $950.43       $1,016.8603   $1,016.87   $1,016.85   $1,017.00