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 $50.26   8.367%   $54.4653   $54.47   $54.45   $54.50  
  Purchase #2 $187.65   4.255%   $195.6345   $195.63   $195.65   $195.60  
  Purchase #3 $151.52   3.566%   $156.9232   $156.92   $156.90   $156.90  
  Purchase #4 $62.84   9.521%   $68.823   $68.82   $68.80   $68.80  
  Purchase #5 $22.29   5.445%   $23.5037   $23.50   $23.50   $23.50  
  Purchase #6 $231.52   7.574%   $249.0553   $249.06   $249.05   $249.10  
  Purchase #7 $26.80   7.290%   $28.7537   $28.75   $28.75   $28.80  
  7 purchase totals = $732.88       $777.1587   $777.15   $777.10   $777.20