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 $206.86   9.560%   $226.6358   $226.64   $226.65   $226.60  
  Purchase #2 $200.47   9.199%   $218.9112   $218.91   $218.90   $218.90  
  Purchase #3 $61.66   6.784%   $65.843   $65.84   $65.85   $65.80  
  Purchase #4 $129.50   11.584%   $144.5013   $144.50   $144.50   $144.50  
  Purchase #5 $203.94   4.179%   $212.4627   $212.46   $212.45   $212.50  
  Purchase #6 $240.57   11.612%   $268.505   $268.51   $268.50   $268.50  
  Purchase #7 $135.28   4.508%   $141.3784   $141.38   $141.40   $141.40  
  7 purchase totals = $1,178.28       $1,278.2374   $1,278.24   $1,278.25   $1,278.20