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 $64.56   5.372%   $68.0282   $68.03   $68.05   $68.00  
  Purchase #2 $56.48   3.521%   $58.4687   $58.47   $58.45   $58.50  
  Purchase #3 $132.95   13.276%   $150.6004   $150.60   $150.60   $150.60  
  Purchase #4 $179.92   8.515%   $195.2402   $195.24   $195.25   $195.20  
  Purchase #5 $75.32   10.819%   $83.4689   $83.47   $83.45   $83.50  
  Purchase #6 $212.93   13.164%   $240.9601   $240.96   $240.95   $241.00  
  Purchase #7 $239.80   11.355%   $267.0293   $267.03   $267.05   $267.00  
  7 purchase totals = $961.96       $1,063.7958   $1,063.80   $1,063.80   $1,063.80