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 $80.84   5.376%   $85.186   $85.19   $85.20   $85.20  
  Purchase #2 $245.64   10.183%   $270.6535   $270.65   $270.65   $270.70  
  Purchase #3 $192.69   11.277%   $214.4197   $214.42   $214.40   $214.40  
  Purchase #4 $162.74   6.337%   $173.0528   $173.05   $173.05   $173.10  
  Purchase #5 $226.78   5.748%   $239.8153   $239.82   $239.80   $239.80  
  Purchase #6 $26.43   13.428%   $29.979   $29.98   $30.00   $30.00  
  Purchase #7 $194.93   3.357%   $201.4738   $201.47   $201.45   $201.50  
  7 purchase totals = $1,130.05       $1,214.5801   $1,214.58   $1,214.55   $1,214.70