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 $186.33   8.280%   $201.7581   $201.76   $201.75   $201.80  
  Purchase #2 $75.68   9.366%   $82.7682   $82.77   $82.75   $82.80  
  Purchase #3 $46.97   13.685%   $53.3978   $53.40   $53.40   $53.40  
  Purchase #4 $112.64   7.726%   $121.3426   $121.34   $121.35   $121.30  
  Purchase #5 $38.48   13.470%   $43.6633   $43.66   $43.65   $43.70  
  Purchase #6 $39.67   10.617%   $43.8818   $43.88   $43.90   $43.90  
  Purchase #7 $204.62   8.512%   $222.0373   $222.04   $222.05   $222.00  
  7 purchase totals = $704.39       $768.8491   $768.85   $768.85   $768.90