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 $143.97   5.379%   $151.7141   $151.71   $151.70   $151.70  
  Purchase #2 $23.56   4.741%   $24.677   $24.68   $24.70   $24.70  
  Purchase #3 $67.32   4.496%   $70.3467   $70.35   $70.35   $70.30  
  Purchase #4 $241.87   3.819%   $251.107   $251.11   $251.10   $251.10  
  Purchase #5 $161.73   5.804%   $171.1168   $171.12   $171.10   $171.10  
  Purchase #6 $147.88   10.731%   $163.749   $163.75   $163.75   $163.70  
  Purchase #7 $50.68   9.708%   $55.6   $55.60   $55.60   $55.60  
  7 purchase totals = $837.01       $888.3106   $888.32   $888.30   $888.20