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 $168.25   11.336%   $187.3228   $187.32   $187.30   $187.30  
  Purchase #2 $243.51   9.156%   $265.8058   $265.81   $265.80   $265.80  
  Purchase #3 $196.98   8.667%   $214.0523   $214.05   $214.05   $214.10  
  Purchase #4 $75.37   5.655%   $79.6322   $79.63   $79.65   $79.60  
  Purchase #5 $33.69   5.365%   $35.4975   $35.50   $35.50   $35.50  
  Purchase #6 $145.86   4.596%   $152.5637   $152.56   $152.55   $152.60  
  Purchase #7 $62.79   12.682%   $70.753   $70.75   $70.75   $70.80  
  7 purchase totals = $926.45       $1,005.6273   $1,005.62   $1,005.60   $1,005.70