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 $71.99   7.266%   $77.2208   $77.22   $77.20   $77.20  
  Purchase #2 $241.68   9.593%   $264.8644   $264.86   $264.85   $264.90  
  Purchase #3 $139.44   6.605%   $148.65   $148.65   $148.65   $148.70  
  Purchase #4 $125.75   4.731%   $131.6992   $131.70   $131.70   $131.70  
  Purchase #5 $89.96   7.227%   $96.4614   $96.46   $96.45   $96.50  
  Purchase #6 $80.30   8.108%   $86.8107   $86.81   $86.80   $86.80  
  Purchase #7 $191.32   7.725%   $206.0995   $206.10   $206.10   $206.10  
  7 purchase totals = $940.44       $1,011.8060   $1,011.80   $1,011.75   $1,011.90