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 $24.69   3.823%   $25.6339   $25.63   $25.65   $25.60  
  Purchase #2 $247.97   9.801%   $272.2735   $272.27   $272.25   $272.30  
  Purchase #3 $70.73   8.869%   $77.003   $77.00   $77.00   $77.00  
  Purchase #4 $27.46   9.746%   $30.1363   $30.14   $30.15   $30.10  
  Purchase #5 $220.35   10.427%   $243.3259   $243.33   $243.35   $243.30  
  Purchase #6 $97.36   12.689%   $109.714   $109.71   $109.70   $109.70  
  Purchase #7 $197.88   5.688%   $209.1354   $209.14   $209.15   $209.10  
  7 purchase totals = $886.44       $967.2220   $967.22   $967.25   $967.10