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 $178.64   12.756%   $201.4273   $201.43   $201.45   $201.40  
  Purchase #2 $61.45   11.391%   $68.4498   $68.45   $68.45   $68.40  
  Purchase #3 $186.59   8.126%   $201.7523   $201.75   $201.75   $201.80  
  Purchase #4 $38.27   5.174%   $40.2501   $40.25   $40.25   $40.30  
  Purchase #5 $59.57   8.771%   $64.7949   $64.79   $64.80   $64.80  
  Purchase #6 $175.94   7.595%   $189.3026   $189.30   $189.30   $189.30  
  Purchase #7 $79.33   11.704%   $88.6148   $88.61   $88.60   $88.60  
  7 purchase totals = $779.79       $854.5918   $854.58   $854.60   $854.60