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 $66.30   11.550%   $73.9577   $73.96   $73.95   $74.00  
  Purchase #2 $196.75   13.276%   $222.8705   $222.87   $222.85   $222.90  
  Purchase #3 $183.43   8.431%   $198.895   $198.90   $198.90   $198.90  
  Purchase #4 $56.38   9.589%   $61.7863   $61.79   $61.80   $61.80  
  Purchase #5 $152.98   8.635%   $166.1898   $166.19   $166.20   $166.20  
  Purchase #6 $130.75   7.150%   $140.0986   $140.10   $140.10   $140.10  
  Purchase #7 $83.64   3.278%   $86.3817   $86.38   $86.40   $86.40  
  7 purchase totals = $870.23       $950.1796   $950.19   $950.20   $950.30