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 $46.71   12.413%   $52.5081   $52.51   $52.50   $52.50  
  Purchase #2 $135.95   11.236%   $151.2253   $151.23   $151.25   $151.20  
  Purchase #3 $34.87   3.858%   $36.2153   $36.22   $36.20   $36.20  
  Purchase #4 $200.48   4.419%   $209.3392   $209.34   $209.35   $209.30  
  Purchase #5 $109.35   12.343%   $122.8471   $122.85   $122.85   $122.80  
  Purchase #6 $199.67   13.537%   $226.6993   $226.70   $226.70   $226.70  
  Purchase #7 $139.85   5.163%   $147.0705   $147.07   $147.05   $147.10  
  7 purchase totals = $866.88       $945.9048   $945.92   $945.90   $945.80