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 $103.77   4.111%   $108.036   $108.04   $108.05   $108.00  
  Purchase #2 $62.88   6.591%   $67.0244   $67.02   $67.00   $67.00  
  Purchase #3 $234.98   7.659%   $252.9771   $252.98   $253.00   $253.00  
  Purchase #4 $191.84   5.473%   $202.3394   $202.34   $202.35   $202.30  
  Purchase #5 $119.39   13.568%   $135.5888   $135.59   $135.60   $135.60  
  Purchase #6 $36.43   10.501%   $40.2555   $40.26   $40.25   $40.30  
  Purchase #7 $233.49   9.272%   $255.1392   $255.14   $255.15   $255.10  
  7 purchase totals = $982.78       $1,061.3604   $1,061.37   $1,061.40   $1,061.30