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 $157.65   10.164%   $173.6735   $173.67   $173.65   $173.70  
  Purchase #2 $195.82   10.111%   $215.6194   $215.62   $215.60   $215.60  
  Purchase #3 $104.44   7.734%   $112.5174   $112.52   $112.50   $112.50  
  Purchase #4 $229.83   13.405%   $260.6387   $260.64   $260.65   $260.60  
  Purchase #5 $155.75   6.602%   $166.0326   $166.03   $166.05   $166.00  
  Purchase #6 $137.28   9.454%   $150.2585   $150.26   $150.25   $150.30  
  Purchase #7 $15.27   6.735%   $16.2984   $16.30   $16.30   $16.30  
  7 purchase totals = $996.04       $1,095.0385   $1,095.04   $1,095.00   $1,095.00