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 $68.92   10.814%   $76.373   $76.37   $76.35   $76.40  
  Purchase #2 $54.60   12.342%   $61.3387   $61.34   $61.35   $61.30  
  Purchase #3 $205.94   12.425%   $231.528   $231.53   $231.55   $231.50  
  Purchase #4 $158.53   10.645%   $175.4055   $175.41   $175.40   $175.40  
  Purchase #5 $159.27   9.769%   $174.8291   $174.83   $174.85   $174.80  
  Purchase #6 $45.28   13.629%   $51.4512   $51.45   $51.45   $51.50  
  Purchase #7 $163.66   9.639%   $179.4352   $179.44   $179.45   $179.40  
  7 purchase totals = $856.20       $950.3607   $950.37   $950.40   $950.30