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 $163.34   13.766%   $185.8254   $185.83   $185.85   $185.80  
  Purchase #2 $83.83   10.135%   $92.3262   $92.33   $92.35   $92.30  
  Purchase #3 $147.33   8.168%   $159.3639   $159.36   $159.35   $159.40  
  Purchase #4 $90.34   5.258%   $95.0901   $95.09   $95.10   $95.10  
  Purchase #5 $203.83   8.452%   $221.0577   $221.06   $221.05   $221.10  
  Purchase #6 $95.25   13.413%   $108.0259   $108.03   $108.05   $108.00  
  Purchase #7 $135.71   13.209%   $153.6359   $153.64   $153.65   $153.60  
  7 purchase totals = $919.63       $1,015.3251   $1,015.34   $1,015.40   $1,015.30