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 $200.72   9.612%   $220.0132   $220.01   $220.00   $220.00  
  Purchase #2 $188.73   12.134%   $211.6305   $211.63   $211.65   $211.60  
  Purchase #3 $167.74   12.606%   $188.8853   $188.89   $188.90   $188.90  
  Purchase #4 $110.28   13.611%   $125.2902   $125.29   $125.30   $125.30  
  Purchase #5 $42.46   3.218%   $43.8264   $43.83   $43.85   $43.80  
  Purchase #6 $115.50   12.599%   $130.0518   $130.05   $130.05   $130.10  
  Purchase #7 $95.62   9.129%   $104.3491   $104.35   $104.35   $104.30  
  7 purchase totals = $921.05       $1,024.0465   $1,024.05   $1,024.10   $1,024.00