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 $56.35   13.179%   $63.7764   $63.78   $63.80   $63.80  
  Purchase #2 $174.97   9.368%   $191.3612   $191.36   $191.35   $191.40  
  Purchase #3 $136.28   7.124%   $145.9886   $145.99   $146.00   $146.00  
  Purchase #4 $52.45   9.115%   $57.2308   $57.23   $57.25   $57.20  
  Purchase #5 $177.59   6.797%   $189.6608   $189.66   $189.65   $189.70  
  Purchase #6 $102.83   10.120%   $113.2364   $113.24   $113.25   $113.20  
  Purchase #7 $195.32   9.562%   $213.9965   $214.00   $214.00   $214.00  
  7 purchase totals = $895.79       $975.2507   $975.26   $975.30   $975.30