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 $67.29   8.790%   $73.2048   $73.20   $73.20   $73.20  
  Purchase #2 $50.58   11.484%   $56.3886   $56.39   $56.40   $56.40  
  Purchase #3 $65.46   12.522%   $73.6569   $73.66   $73.65   $73.70  
  Purchase #4 $205.73   3.195%   $212.3031   $212.30   $212.30   $212.30  
  Purchase #5 $8.40   8.461%   $9.1107   $9.11   $9.10   $9.10  
  Purchase #6 $84.48   11.661%   $94.3312   $94.33   $94.35   $94.30  
  Purchase #7 $210.65   10.703%   $233.1959   $233.20   $233.20   $233.20  
  7 purchase totals = $692.59       $752.1912   $752.19   $752.20   $752.20