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 $90.66   5.714%   $95.8403   $95.84   $95.85   $95.80  
  Purchase #2 $226.95   9.126%   $247.6615   $247.66   $247.65   $247.70  
  Purchase #3 $93.34   5.629%   $98.5941   $98.59   $98.60   $98.60  
  Purchase #4 $212.67   7.742%   $229.1349   $229.13   $229.15   $229.10  
  Purchase #5 $55.37   5.537%   $58.4358   $58.44   $58.45   $58.40  
  Purchase #6 $56.27   13.137%   $63.6622   $63.66   $63.65   $63.70  
  Purchase #7 $68.92   4.570%   $72.0696   $72.07   $72.05   $72.10  
  7 purchase totals = $804.18       $865.3984   $865.39   $865.40   $865.40