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 $247.59   11.711%   $276.5853   $276.59   $276.60   $276.60  
  Purchase #2 $70.44   7.582%   $75.7808   $75.78   $75.80   $75.80  
  Purchase #3 $56.83   7.726%   $61.2207   $61.22   $61.20   $61.20  
  Purchase #4 $172.38   13.180%   $195.0997   $195.10   $195.10   $195.10  
  Purchase #5 $143.45   13.298%   $162.526   $162.53   $162.55   $162.50  
  Purchase #6 $99.59   3.110%   $102.6872   $102.69   $102.70   $102.70  
  Purchase #7 $17.62   8.170%   $19.0596   $19.06   $19.05   $19.10  
  7 purchase totals = $807.90       $892.9593   $892.97   $893.00   $893.00