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 $67.57   11.733%   $75.498   $75.50   $75.50   $75.50  
  Purchase #2 $39.86   5.383%   $42.0057   $42.01   $42.00   $42.00  
  Purchase #3 $145.50   13.855%   $165.659   $165.66   $165.65   $165.70  
  Purchase #4 $250.64   3.646%   $259.7783   $259.78   $259.80   $259.80  
  Purchase #5 $208.29   7.673%   $224.2721   $224.27   $224.25   $224.30  
  Purchase #6 $204.74   13.607%   $232.599   $232.60   $232.60   $232.60  
  Purchase #7 $58.75   7.222%   $62.9929   $62.99   $63.00   $63.00  
  7 purchase totals = $975.35       $1,062.8050   $1,062.81   $1,062.80   $1,062.90