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 $104.78   8.530%   $113.7177   $113.72   $113.70   $113.70  
  Purchase #2 $70.95   6.631%   $75.6547   $75.65   $75.65   $75.70  
  Purchase #3 $162.78   8.825%   $177.1453   $177.15   $177.15   $177.10  
  Purchase #4 $212.87   8.538%   $231.0448   $231.04   $231.05   $231.00  
  Purchase #5 $200.81   13.296%   $227.5097   $227.51   $227.50   $227.50  
  Purchase #6 $235.90   9.640%   $258.6408   $258.64   $258.65   $258.60  
  Purchase #7 $38.92   11.522%   $43.4044   $43.40   $43.40   $43.40  
  7 purchase totals = $1,027.01       $1,127.1174   $1,127.11   $1,127.10   $1,127.00