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 $92.89   11.155%   $103.2519   $103.25   $103.25   $103.30  
  Purchase #2 $232.72   13.617%   $264.4095   $264.41   $264.40   $264.40  
  Purchase #3 $34.67   6.399%   $36.8885   $36.89   $36.90   $36.90  
  Purchase #4 $84.97   7.670%   $91.4872   $91.49   $91.50   $91.50  
  Purchase #5 $17.54   6.213%   $18.6298   $18.63   $18.65   $18.60  
  Purchase #6 $213.70   5.793%   $226.0796   $226.08   $226.10   $226.10  
  Purchase #7 $129.98   5.202%   $136.7416   $136.74   $136.75   $136.70  
  7 purchase totals = $806.47       $877.4881   $877.49   $877.55   $877.50