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 $166.37   10.473%   $183.7939   $183.79   $183.80   $183.80  
  Purchase #2 $153.47   13.721%   $174.5276   $174.53   $174.55   $174.50  
  Purchase #3 $56.26   8.203%   $60.875   $60.88   $60.90   $60.90  
  Purchase #4 $200.71   3.256%   $207.2451   $207.25   $207.25   $207.20  
  Purchase #5 $138.63   9.544%   $151.8608   $151.86   $151.85   $151.90  
  Purchase #6 $142.63   11.590%   $159.1608   $159.16   $159.15   $159.20  
  Purchase #7 $153.48   5.103%   $161.3121   $161.31   $161.30   $161.30  
  7 purchase totals = $1,011.55       $1,098.7753   $1,098.78   $1,098.80   $1,098.80