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 $89.61   6.451%   $95.3907   $95.39   $95.40   $95.40  
  Purchase #2 $226.85   8.515%   $246.1663   $246.17   $246.15   $246.20  
  Purchase #3 $84.97   9.497%   $93.0396   $93.04   $93.05   $93.00  
  Purchase #4 $110.84   8.470%   $120.2281   $120.23   $120.25   $120.20  
  Purchase #5 $171.30   4.661%   $179.2843   $179.28   $179.30   $179.30  
  Purchase #6 $152.25   8.243%   $164.8   $164.80   $164.80   $164.80  
  Purchase #7 $49.37   4.597%   $51.6395   $51.64   $51.65   $51.60  
  7 purchase totals = $885.19       $950.5485   $950.55   $950.60   $950.50