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 $158.26   10.517%   $174.9042   $174.90   $174.90   $174.90  
  Purchase #2 $79.85   6.846%   $85.3165   $85.32   $85.30   $85.30  
  Purchase #3 $163.62   8.587%   $177.67   $177.67   $177.65   $177.70  
  Purchase #4 $126.85   9.103%   $138.3972   $138.40   $138.40   $138.40  
  Purchase #5 $230.87   3.791%   $239.6223   $239.62   $239.60   $239.60  
  Purchase #6 $187.62   6.149%   $199.1568   $199.16   $199.15   $199.20  
  Purchase #7 $64.94   12.677%   $73.1724   $73.17   $73.15   $73.20  
  7 purchase totals = $1,012.01       $1,088.2394   $1,088.24   $1,088.15   $1,088.30