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 $32.25   8.561%   $35.0109   $35.01   $35.00   $35.00  
  Purchase #2 $191.88   10.804%   $212.6107   $212.61   $212.60   $212.60  
  Purchase #3 $15.37   11.149%   $17.0836   $17.08   $17.10   $17.10  
  Purchase #4 $184.53   9.364%   $201.8094   $201.81   $201.80   $201.80  
  Purchase #5 $96.97   13.296%   $109.8631   $109.86   $109.85   $109.90  
  Purchase #6 $248.29   11.255%   $276.235   $276.24   $276.25   $276.20  
  Purchase #7 $172.93   11.862%   $193.443   $193.44   $193.45   $193.40  
  7 purchase totals = $942.22       $1,046.0557   $1,046.05   $1,046.05   $1,046.00