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 $162.77   12.566%   $183.2237   $183.22   $183.20   $183.20  
  Purchase #2 $117.93   3.823%   $122.4385   $122.44   $122.45   $122.40  
  Purchase #3 $52.70   9.486%   $57.6991   $57.70   $57.70   $57.70  
  Purchase #4 $224.53   8.281%   $243.1233   $243.12   $243.10   $243.10  
  Purchase #5 $56.46   6.260%   $59.9944   $59.99   $60.00   $60.00  
  Purchase #6 $192.93   7.626%   $207.6428   $207.64   $207.65   $207.60  
  Purchase #7 $218.53   7.412%   $234.7274   $234.73   $234.75   $234.70  
  7 purchase totals = $1,025.85       $1,108.8492   $1,108.84   $1,108.85   $1,108.70