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 $232.56   8.874%   $253.1974   $253.20   $253.20   $253.20  
  Purchase #2 $10.64   9.716%   $11.6738   $11.67   $11.65   $11.70  
  Purchase #3 $219.39   11.292%   $244.1635   $244.16   $244.15   $244.20  
  Purchase #4 $195.66   4.670%   $204.7973   $204.80   $204.80   $204.80  
  Purchase #5 $83.92   4.307%   $87.5344   $87.53   $87.55   $87.50  
  Purchase #6 $133.90   6.517%   $142.6263   $142.63   $142.65   $142.60  
  Purchase #7 $52.78   13.743%   $60.0336   $60.03   $60.05   $60.00  
  7 purchase totals = $928.85       $1,004.0263   $1,004.02   $1,004.05   $1,004.00