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 $96.87   10.212%   $106.7624   $106.76   $106.75   $106.80  
  Purchase #2 $42.78   9.384%   $46.7945   $46.79   $46.80   $46.80  
  Purchase #3 $229.50   10.243%   $253.0077   $253.01   $253.00   $253.00  
  Purchase #4 $174.30   9.435%   $190.7452   $190.75   $190.75   $190.70  
  Purchase #5 $170.87   12.426%   $192.1023   $192.10   $192.10   $192.10  
  Purchase #6 $115.43   6.550%   $122.9907   $122.99   $123.00   $123.00  
  Purchase #7 $122.61   10.663%   $135.6839   $135.68   $135.70   $135.70  
  7 purchase totals = $952.36       $1,048.0867   $1,048.08   $1,048.10   $1,048.10