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 $168.87   8.740%   $183.6292   $183.63   $183.65   $183.60  
  Purchase #2 $240.62   7.450%   $258.5462   $258.55   $258.55   $258.50  
  Purchase #3 $176.33   6.232%   $187.3189   $187.32   $187.30   $187.30  
  Purchase #4 $244.34   4.623%   $255.6358   $255.64   $255.65   $255.60  
  Purchase #5 $15.96   6.534%   $17.0028   $17.00   $17.00   $17.00  
  Purchase #6 $89.67   7.432%   $96.3343   $96.33   $96.35   $96.30  
  Purchase #7 $212.45   10.138%   $233.9882   $233.99   $234.00   $234.00  
  7 purchase totals = $1,148.24       $1,232.4554   $1,232.46   $1,232.50   $1,232.30