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 $70.47   8.461%   $76.4325   $76.43   $76.45   $76.40  
  Purchase #2 $239.64   5.104%   $251.8712   $251.87   $251.85   $251.90  
  Purchase #3 $27.30   12.864%   $30.8119   $30.81   $30.80   $30.80  
  Purchase #4 $108.44   8.684%   $117.8569   $117.86   $117.85   $117.90  
  Purchase #5 $191.44   13.657%   $217.585   $217.59   $217.60   $217.60  
  Purchase #6 $129.50   6.644%   $138.104   $138.10   $138.10   $138.10  
  Purchase #7 $196.56   3.582%   $203.6008   $203.60   $203.60   $203.60  
  7 purchase totals = $963.35       $1,036.2623   $1,036.26   $1,036.25   $1,036.30