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 $98.26   6.132%   $104.2853   $104.29   $104.30   $104.30  
  Purchase #2 $113.81   11.609%   $127.0222   $127.02   $127.00   $127.00  
  Purchase #3 $57.50   5.222%   $60.5027   $60.50   $60.50   $60.50  
  Purchase #4 $30.73   9.808%   $33.744   $33.74   $33.75   $33.70  
  Purchase #5 $245.46   11.300%   $273.197   $273.20   $273.20   $273.20  
  Purchase #6 $127.41   6.160%   $135.2585   $135.26   $135.25   $135.30  
  Purchase #7 $28.70   8.418%   $31.116   $31.12   $31.10   $31.10  
  7 purchase totals = $701.87       $765.1257   $765.13   $765.10   $765.10