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 $86.63   5.763%   $91.6225   $91.62   $91.60   $91.60  
  Purchase #2 $193.79   3.648%   $200.8595   $200.86   $200.85   $200.90  
  Purchase #3 $86.54   3.224%   $89.33   $89.33   $89.35   $89.30  
  Purchase #4 $169.35   4.368%   $176.7472   $176.75   $176.75   $176.70  
  Purchase #5 $56.98   11.831%   $63.7213   $63.72   $63.70   $63.70  
  Purchase #6 $43.99   11.365%   $48.9895   $48.99   $49.00   $49.00  
  Purchase #7 $80.27   10.786%   $88.9279   $88.93   $88.95   $88.90  
  7 purchase totals = $717.55       $760.1979   $760.20   $760.20   $760.10