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 $246.80   7.573%   $265.4902   $265.49   $265.50   $265.50  
  Purchase #2 $60.55   13.547%   $68.7527   $68.75   $68.75   $68.80  
  Purchase #3 $127.26   10.312%   $140.3831   $140.38   $140.40   $140.40  
  Purchase #4 $12.58   10.556%   $13.9079   $13.91   $13.90   $13.90  
  Purchase #5 $128.51   3.211%   $132.6365   $132.64   $132.65   $132.60  
  Purchase #6 $24.76   3.694%   $25.6746   $25.67   $25.65   $25.70  
  Purchase #7 $219.76   4.211%   $229.0141   $229.01   $229.00   $229.00  
  7 purchase totals = $820.22       $875.8591   $875.85   $875.85   $875.90