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 $123.91   7.554%   $133.2702   $133.27   $133.25   $133.30  
  Purchase #2 $69.96   10.741%   $77.4744   $77.47   $77.45   $77.50  
  Purchase #3 $116.59   5.242%   $122.7016   $122.70   $122.70   $122.70  
  Purchase #4 $154.99   9.399%   $169.5575   $169.56   $169.55   $169.60  
  Purchase #5 $236.89   11.234%   $263.5022   $263.50   $263.50   $263.50  
  Purchase #6 $212.33   13.506%   $241.0073   $241.01   $241.00   $241.00  
  Purchase #7 $5.70   6.242%   $6.0558   $6.06   $6.05   $6.10  
  7 purchase totals = $920.37       $1,013.5690   $1,013.57   $1,013.50   $1,013.70