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 $22.65   8.530%   $24.582   $24.58   $24.60   $24.60  
  Purchase #2 $184.57   4.352%   $192.6025   $192.60   $192.60   $192.60  
  Purchase #3 $97.85   13.744%   $111.2985   $111.30   $111.30   $111.30  
  Purchase #4 $129.97   8.204%   $140.6327   $140.63   $140.65   $140.60  
  Purchase #5 $133.51   5.503%   $140.8571   $140.86   $140.85   $140.90  
  Purchase #6 $53.83   13.227%   $60.9501   $60.95   $60.95   $61.00  
  Purchase #7 $159.55   11.205%   $177.4276   $177.43   $177.45   $177.40  
  7 purchase totals = $781.93       $848.3505   $848.35   $848.40   $848.40