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 $88.69   7.846%   $95.6486   $95.65   $95.65   $95.60  
  Purchase #2 $6.50   3.746%   $6.7435   $6.74   $6.75   $6.70  
  Purchase #3 $27.90   7.121%   $29.8868   $29.89   $29.90   $29.90  
  Purchase #4 $205.40   3.556%   $212.704   $212.70   $212.70   $212.70  
  Purchase #5 $73.46   12.523%   $82.6594   $82.66   $82.65   $82.70  
  Purchase #6 $88.91   11.840%   $99.4369   $99.44   $99.45   $99.40  
  Purchase #7 $216.73   8.359%   $234.8465   $234.85   $234.85   $234.80  
  7 purchase totals = $707.59       $761.9257   $761.93   $761.95   $761.80