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 $81.83   3.833%   $84.9665   $84.97   $84.95   $85.00  
  Purchase #2 $232.27   4.471%   $242.6548   $242.65   $242.65   $242.70  
  Purchase #3 $242.72   11.337%   $270.2372   $270.24   $270.25   $270.20  
  Purchase #4 $201.57   4.142%   $209.919   $209.92   $209.90   $209.90  
  Purchase #5 $100.72   9.238%   $110.0245   $110.02   $110.00   $110.00  
  Purchase #6 $190.46   12.481%   $214.2313   $214.23   $214.25   $214.20  
  Purchase #7 $244.99   7.411%   $263.1462   $263.15   $263.15   $263.10  
  7 purchase totals = $1,294.56       $1,395.1795   $1,395.18   $1,395.15   $1,395.10