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 $10.30   3.459%   $10.6563   $10.66   $10.65   $10.70  
  Purchase #2 $215.48   3.801%   $223.6704   $223.67   $223.65   $223.70  
  Purchase #3 $64.79   4.328%   $67.5941   $67.59   $67.60   $67.60  
  Purchase #4 $17.58   6.796%   $18.7747   $18.77   $18.75   $18.80  
  Purchase #5 $94.42   7.309%   $101.3212   $101.32   $101.30   $101.30  
  Purchase #6 $16.53   7.200%   $17.7202   $17.72   $17.70   $17.70  
  Purchase #7 $178.61   11.203%   $198.6197   $198.62   $198.60   $198.60  
  7 purchase totals = $597.71       $638.3566   $638.35   $638.25   $638.40