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 $222.58   13.670%   $253.0067   $253.01   $253.00   $253.00  
  Purchase #2 $221.77   10.415%   $244.8673   $244.87   $244.85   $244.90  
  Purchase #3 $33.50   3.573%   $34.697   $34.70   $34.70   $34.70  
  Purchase #4 $47.70   5.677%   $50.4079   $50.41   $50.40   $50.40  
  Purchase #5 $133.59   5.546%   $140.9989   $141.00   $141.00   $141.00  
  Purchase #6 $153.59   7.454%   $165.0386   $165.04   $165.05   $165.00  
  Purchase #7 $110.30   7.269%   $118.3177   $118.32   $118.30   $118.30  
  7 purchase totals = $923.03       $1,007.3341   $1,007.35   $1,007.30   $1,007.30