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 $156.97   8.108%   $169.6971   $169.70   $169.70   $169.70  
  Purchase #2 $91.64   10.515%   $101.2759   $101.28   $101.30   $101.30  
  Purchase #3 $209.45   5.788%   $221.573   $221.57   $221.55   $221.60  
  Purchase #4 $109.51   7.466%   $117.686   $117.69   $117.70   $117.70  
  Purchase #5 $48.68   9.834%   $53.4672   $53.47   $53.45   $53.50  
  Purchase #6 $48.59   11.663%   $54.2571   $54.26   $54.25   $54.30  
  Purchase #7 $194.53   6.439%   $207.0558   $207.06   $207.05   $207.10  
  7 purchase totals = $859.37       $925.0121   $925.03   $925.00   $925.20