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 $86.58   9.522%   $94.8241   $94.82   $94.80   $94.80  
  Purchase #2 $137.91   7.715%   $148.5498   $148.55   $148.55   $148.50  
  Purchase #3 $80.29   6.551%   $85.5498   $85.55   $85.55   $85.50  
  Purchase #4 $145.43   6.366%   $154.6881   $154.69   $154.70   $154.70  
  Purchase #5 $39.53   8.815%   $43.0146   $43.01   $43.00   $43.00  
  Purchase #6 $191.76   6.729%   $204.6635   $204.66   $204.65   $204.70  
  Purchase #7 $235.82   8.553%   $255.9897   $255.99   $256.00   $256.00  
  7 purchase totals = $917.32       $987.2796   $987.27   $987.25   $987.20