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 $186.65   4.479%   $195.0101   $195.01   $195.00   $195.00  
  Purchase #2 $247.37   13.208%   $280.0426   $280.04   $280.05   $280.00  
  Purchase #3 $214.78   9.641%   $235.4869   $235.49   $235.50   $235.50  
  Purchase #4 $185.68   4.678%   $194.3661   $194.37   $194.35   $194.40  
  Purchase #5 $95.27   10.341%   $105.1219   $105.12   $105.10   $105.10  
  Purchase #6 $231.30   4.372%   $241.4124   $241.41   $241.40   $241.40  
  Purchase #7 $96.25   12.579%   $108.3573   $108.36   $108.35   $108.40  
  7 purchase totals = $1,257.30       $1,359.7973   $1,359.80   $1,359.75   $1,359.80