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 $244.34   13.147%   $276.4634   $276.46   $276.45   $276.50  
  Purchase #2 $178.79   7.694%   $192.5461   $192.55   $192.55   $192.50  
  Purchase #3 $224.26   5.463%   $236.5113   $236.51   $236.50   $236.50  
  Purchase #4 $88.85   5.840%   $94.0388   $94.04   $94.05   $94.00  
  Purchase #5 $43.35   3.435%   $44.8391   $44.84   $44.85   $44.80  
  Purchase #6 $5.54   12.802%   $6.2492   $6.25   $6.25   $6.20  
  Purchase #7 $229.71   6.484%   $244.6044   $244.60   $244.60   $244.60  
  7 purchase totals = $1,014.84       $1,095.2523   $1,095.25   $1,095.25   $1,095.10