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 $67.82   8.290%   $73.4423   $73.44   $73.45   $73.40  
  Purchase #2 $210.56   8.133%   $227.6848   $227.68   $227.70   $227.70  
  Purchase #3 $184.68   13.170%   $209.0024   $209.00   $209.00   $209.00  
  Purchase #4 $189.77   6.699%   $202.4827   $202.48   $202.50   $202.50  
  Purchase #5 $25.88   11.115%   $28.7566   $28.76   $28.75   $28.80  
  Purchase #6 $147.92   9.579%   $162.0893   $162.09   $162.10   $162.10  
  Purchase #7 $186.29   11.528%   $207.7655   $207.77   $207.75   $207.80  
  7 purchase totals = $1,012.92       $1,111.2236   $1,111.22   $1,111.25   $1,111.30