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 $58.81   4.590%   $61.5094   $61.51   $61.50   $61.50  
  Purchase #2 $151.60   9.619%   $166.1824   $166.18   $166.20   $166.20  
  Purchase #3 $109.53   10.114%   $120.6079   $120.61   $120.60   $120.60  
  Purchase #4 $54.95   12.355%   $61.7391   $61.74   $61.75   $61.70  
  Purchase #5 $133.60   12.628%   $150.471   $150.47   $150.45   $150.50  
  Purchase #6 $97.87   8.238%   $105.9325   $105.93   $105.95   $105.90  
  Purchase #7 $228.88   4.581%   $239.365   $239.37   $239.35   $239.40  
  7 purchase totals = $835.24       $905.8073   $905.81   $905.80   $905.80