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 $211.42   10.454%   $233.5218   $233.52   $233.50   $233.50  
  Purchase #2 $187.86   11.594%   $209.6405   $209.64   $209.65   $209.60  
  Purchase #3 $44.88   9.855%   $49.3029   $49.30   $49.30   $49.30  
  Purchase #4 $87.99   8.798%   $95.7314   $95.73   $95.75   $95.70  
  Purchase #5 $203.70   3.178%   $210.1736   $210.17   $210.15   $210.20  
  Purchase #6 $213.74   6.574%   $227.7913   $227.79   $227.80   $227.80  
  Purchase #7 $32.96   6.618%   $35.1413   $35.14   $35.15   $35.10  
  7 purchase totals = $982.55       $1,061.3028   $1,061.29   $1,061.30   $1,061.20