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 $59.41   8.748%   $64.6072   $64.61   $64.60   $64.60  
  Purchase #2 $206.33   11.244%   $229.5297   $229.53   $229.55   $229.50  
  Purchase #3 $205.56   7.411%   $220.7941   $220.79   $220.80   $220.80  
  Purchase #4 $165.61   11.362%   $184.4266   $184.43   $184.45   $184.40  
  Purchase #5 $73.40   4.697%   $76.8476   $76.85   $76.85   $76.80  
  Purchase #6 $235.56   5.167%   $247.7314   $247.73   $247.75   $247.70  
  Purchase #7 $38.94   3.612%   $40.3465   $40.35   $40.35   $40.30  
  7 purchase totals = $984.81       $1,064.2831   $1,064.29   $1,064.35   $1,064.10