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 $202.89   10.396%   $223.9824   $223.98   $224.00   $224.00  
  Purchase #2 $12.26   6.642%   $13.0743   $13.07   $13.05   $13.10  
  Purchase #3 $85.98   11.146%   $95.5633   $95.56   $95.55   $95.60  
  Purchase #4 $157.65   3.147%   $162.6112   $162.61   $162.60   $162.60  
  Purchase #5 $222.64   8.486%   $241.5332   $241.53   $241.55   $241.50  
  Purchase #6 $188.38   8.541%   $204.4695   $204.47   $204.45   $204.50  
  Purchase #7 $78.59   6.169%   $83.4382   $83.44   $83.45   $83.40  
  7 purchase totals = $948.39       $1,024.6721   $1,024.66   $1,024.65   $1,024.70