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 $174.55   5.873%   $184.8013   $184.80   $184.80   $184.80  
  Purchase #2 $125.44   13.120%   $141.8977   $141.90   $141.90   $141.90  
  Purchase #3 $207.85   8.268%   $225.035   $225.04   $225.05   $225.00  
  Purchase #4 $43.83   9.729%   $48.0942   $48.09   $48.10   $48.10  
  Purchase #5 $241.83   13.539%   $274.5714   $274.57   $274.55   $274.60  
  Purchase #6 $124.86   8.799%   $135.8464   $135.85   $135.85   $135.80  
  Purchase #7 $29.66   13.246%   $33.5888   $33.59   $33.60   $33.60  
  7 purchase totals = $948.02       $1,043.8348   $1,043.84   $1,043.85   $1,043.80