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 $36.62   10.743%   $40.5541   $40.55   $40.55   $40.60  
  Purchase #2 $109.60   9.117%   $119.5922   $119.59   $119.60   $119.60  
  Purchase #3 $141.84   5.190%   $149.2015   $149.20   $149.20   $149.20  
  Purchase #4 $163.47   8.477%   $177.3274   $177.33   $177.35   $177.30  
  Purchase #5 $52.74   10.248%   $58.1448   $58.14   $58.15   $58.10  
  Purchase #6 $222.55   11.263%   $247.6158   $247.62   $247.60   $247.60  
  Purchase #7 $211.83   6.369%   $225.3215   $225.32   $225.30   $225.30  
  7 purchase totals = $938.65       $1,017.7573   $1,017.75   $1,017.75   $1,017.70