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 $55.94   9.527%   $61.2694   $61.27   $61.25   $61.30  
  Purchase #2 $133.57   8.489%   $144.9088   $144.91   $144.90   $144.90  
  Purchase #3 $216.65   11.232%   $240.9841   $240.98   $241.00   $241.00  
  Purchase #4 $60.99   12.563%   $68.6522   $68.65   $68.65   $68.70  
  Purchase #5 $235.48   3.739%   $244.2846   $244.28   $244.30   $244.30  
  Purchase #6 $165.74   5.473%   $174.811   $174.81   $174.80   $174.80  
  Purchase #7 $194.94   6.620%   $207.845   $207.85   $207.85   $207.80  
  7 purchase totals = $1,063.31       $1,142.7551   $1,142.75   $1,142.75   $1,142.80