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 $96.79   5.784%   $102.3883   $102.39   $102.40   $102.40  
  Purchase #2 $219.50   9.249%   $239.8016   $239.80   $239.80   $239.80  
  Purchase #3 $86.53   8.262%   $93.6791   $93.68   $93.70   $93.70  
  Purchase #4 $191.88   13.388%   $217.5689   $217.57   $217.55   $217.60  
  Purchase #5 $48.67   13.598%   $55.2881   $55.29   $55.30   $55.30  
  Purchase #6 $122.82   12.454%   $138.116   $138.12   $138.10   $138.10  
  Purchase #7 $184.42   4.467%   $192.658   $192.66   $192.65   $192.70  
  7 purchase totals = $950.61       $1,039.5000   $1,039.51   $1,039.50   $1,039.60