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 $86.97   7.241%   $93.2675   $93.27   $93.25   $93.30  
  Purchase #2 $188.97   11.132%   $210.0061   $210.01   $210.00   $210.00  
  Purchase #3 $177.96   3.158%   $183.58   $183.58   $183.60   $183.60  
  Purchase #4 $194.61   11.159%   $216.3265   $216.33   $216.35   $216.30  
  Purchase #5 $245.89   3.519%   $254.5429   $254.54   $254.55   $254.50  
  Purchase #6 $235.87   5.829%   $249.6189   $249.62   $249.60   $249.60  
  Purchase #7 $20.85   5.833%   $22.0662   $22.07   $22.05   $22.10  
  7 purchase totals = $1,151.12       $1,229.4081   $1,229.42   $1,229.40   $1,229.40