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 $37.29   11.751%   $41.6719   $41.67   $41.65   $41.70  
  Purchase #2 $185.98   5.737%   $196.6497   $196.65   $196.65   $196.60  
  Purchase #3 $198.31   11.221%   $220.5624   $220.56   $220.55   $220.60  
  Purchase #4 $250.33   10.538%   $276.7098   $276.71   $276.70   $276.70  
  Purchase #5 $77.41   5.213%   $81.4454   $81.45   $81.45   $81.40  
  Purchase #6 $239.65   11.157%   $266.3878   $266.39   $266.40   $266.40  
  Purchase #7 $222.92   11.555%   $248.6784   $248.68   $248.70   $248.70  
  7 purchase totals = $1,211.89       $1,332.1054   $1,332.11   $1,332.10   $1,332.10