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 $86.80   10.357%   $95.7899   $95.79   $95.80   $95.80  
  Purchase #2 $72.86   12.531%   $81.9901   $81.99   $82.00   $82.00  
  Purchase #3 $163.78   6.124%   $173.8099   $173.81   $173.80   $173.80  
  Purchase #4 $145.70   4.824%   $152.7286   $152.73   $152.75   $152.70  
  Purchase #5 $7.59   5.826%   $8.0322   $8.03   $8.05   $8.00  
  Purchase #6 $220.29   13.511%   $250.0534   $250.05   $250.05   $250.10  
  Purchase #7 $232.72   10.176%   $256.4016   $256.40   $256.40   $256.40  
  7 purchase totals = $929.74       $1,018.8057   $1,018.80   $1,018.85   $1,018.80