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 $97.34   10.241%   $107.3086   $107.31   $107.30   $107.30  
  Purchase #2 $231.93   11.562%   $258.7457   $258.75   $258.75   $258.70  
  Purchase #3 $164.85   7.284%   $176.8577   $176.86   $176.85   $176.90  
  Purchase #4 $109.53   5.847%   $115.9342   $115.93   $115.95   $115.90  
  Purchase #5 $20.84   11.423%   $23.2206   $23.22   $23.20   $23.20  
  Purchase #6 $117.89   12.234%   $132.3127   $132.31   $132.30   $132.30  
  Purchase #7 $220.85   11.678%   $246.6409   $246.64   $246.65   $246.60  
  7 purchase totals = $963.23       $1,061.0204   $1,061.02   $1,061.00   $1,060.90