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 $182.57   11.163%   $202.9503   $202.95   $202.95   $203.00  
  Purchase #2 $75.41   10.173%   $83.0815   $83.08   $83.10   $83.10  
  Purchase #3 $21.42   6.587%   $22.8309   $22.83   $22.85   $22.80  
  Purchase #4 $28.48   13.586%   $32.3493   $32.35   $32.35   $32.30  
  Purchase #5 $201.72   10.532%   $222.9652   $222.97   $222.95   $223.00  
  Purchase #6 $94.47   9.823%   $103.7498   $103.75   $103.75   $103.70  
  Purchase #7 $229.71   3.106%   $236.8448   $236.84   $236.85   $236.80  
  7 purchase totals = $833.78       $904.7718   $904.77   $904.80   $904.70