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 $74.48   7.354%   $79.9573   $79.96   $79.95   $80.00  
  Purchase #2 $80.66   13.851%   $91.8322   $91.83   $91.85   $91.80  
  Purchase #3 $117.69   7.545%   $126.5697   $126.57   $126.55   $126.60  
  Purchase #4 $164.88   4.283%   $171.9418   $171.94   $171.95   $171.90  
  Purchase #5 $214.98   7.602%   $231.3228   $231.32   $231.30   $231.30  
  Purchase #6 $194.74   6.109%   $206.6367   $206.64   $206.65   $206.60  
  Purchase #7 $145.54   10.331%   $160.5757   $160.58   $160.60   $160.60  
  7 purchase totals = $992.97       $1,068.8362   $1,068.84   $1,068.85   $1,068.80