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 $88.53   8.107%   $95.7071   $95.71   $95.70   $95.70  
  Purchase #2 $144.80   8.191%   $156.6606   $156.66   $156.65   $156.70  
  Purchase #3 $19.77   6.826%   $21.1195   $21.12   $21.10   $21.10  
  Purchase #4 $166.64   4.864%   $174.7454   $174.75   $174.75   $174.70  
  Purchase #5 $57.66   10.834%   $63.9069   $63.91   $63.90   $63.90  
  Purchase #6 $188.72   10.799%   $209.0999   $209.10   $209.10   $209.10  
  Purchase #7 $77.78   6.142%   $82.5572   $82.56   $82.55   $82.60  
  7 purchase totals = $743.90       $803.7966   $803.81   $803.75   $803.80