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 $96.34   8.132%   $104.1744   $104.17   $104.15   $104.20  
  Purchase #2 $202.49   10.864%   $224.4885   $224.49   $224.50   $224.50  
  Purchase #3 $206.61   3.544%   $213.9323   $213.93   $213.95   $213.90  
  Purchase #4 $60.86   10.336%   $67.1505   $67.15   $67.15   $67.20  
  Purchase #5 $164.43   5.397%   $173.3043   $173.30   $173.30   $173.30  
  Purchase #6 $48.34   9.150%   $52.7631   $52.76   $52.75   $52.80  
  Purchase #7 $204.91   9.724%   $224.8354   $224.84   $224.85   $224.80  
  7 purchase totals = $983.98       $1,060.6485   $1,060.64   $1,060.65   $1,060.70