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 $236.94   6.363%   $252.0165   $252.02   $252.00   $252.00  
  Purchase #2 $106.85   4.416%   $111.5685   $111.57   $111.55   $111.60  
  Purchase #3 $112.68   4.131%   $117.3348   $117.33   $117.35   $117.30  
  Purchase #4 $206.81   5.531%   $218.2487   $218.25   $218.25   $218.20  
  Purchase #5 $226.37   5.843%   $239.5968   $239.60   $239.60   $239.60  
  Purchase #6 $57.29   8.282%   $62.0348   $62.03   $62.05   $62.00  
  Purchase #7 $177.50   6.251%   $188.5955   $188.60   $188.60   $188.60  
  7 purchase totals = $1,124.44       $1,189.3956   $1,189.40   $1,189.40   $1,189.30