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 $102.51   10.502%   $113.2756   $113.28   $113.30   $113.30  
  Purchase #2 $143.41   6.371%   $152.5467   $152.55   $152.55   $152.50  
  Purchase #3 $119.78   8.528%   $129.9948   $129.99   $130.00   $130.00  
  Purchase #4 $40.85   12.635%   $46.0114   $46.01   $46.00   $46.00  
  Purchase #5 $65.86   11.645%   $73.5294   $73.53   $73.55   $73.50  
  Purchase #6 $5.51   13.569%   $6.2577   $6.26   $6.25   $6.30  
  Purchase #7 $158.32   9.658%   $173.6105   $173.61   $173.60   $173.60  
  7 purchase totals = $636.24       $695.2261   $695.23   $695.25   $695.20