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 $85.98   6.556%   $91.6168   $91.62   $91.60   $91.60  
  Purchase #2 $6.99   8.722%   $7.5997   $7.60   $7.60   $7.60  
  Purchase #3 $26.77   6.443%   $28.4948   $28.49   $28.50   $28.50  
  Purchase #4 $178.54   11.355%   $198.8132   $198.81   $198.80   $198.80  
  Purchase #5 $246.51   7.663%   $265.4001   $265.40   $265.40   $265.40  
  Purchase #6 $206.89   10.547%   $228.7107   $228.71   $228.70   $228.70  
  Purchase #7 $200.65   6.609%   $213.911   $213.91   $213.90   $213.90  
  7 purchase totals = $952.33       $1,034.5463   $1,034.54   $1,034.50   $1,034.50