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 $15.69   3.232%   $16.1971   $16.20   $16.20   $16.20  
  Purchase #2 $233.77   11.237%   $260.0387   $260.04   $260.05   $260.00  
  Purchase #3 $218.90   12.767%   $246.847   $246.85   $246.85   $246.80  
  Purchase #4 $64.71   9.604%   $70.9247   $70.92   $70.90   $70.90  
  Purchase #5 $131.38   3.414%   $135.8653   $135.87   $135.85   $135.90  
  Purchase #6 $61.78   6.550%   $65.8266   $65.83   $65.85   $65.80  
  Purchase #7 $202.54   12.794%   $228.453   $228.45   $228.45   $228.50  
  7 purchase totals = $928.77       $1,024.1524   $1,024.16   $1,024.15   $1,024.10