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 $235.82   11.354%   $262.595   $262.60   $262.60   $262.60  
  Purchase #2 $42.84   13.449%   $48.6016   $48.60   $48.60   $48.60  
  Purchase #3 $55.77   9.660%   $61.1574   $61.16   $61.15   $61.20  
  Purchase #4 $151.41   9.442%   $165.7061   $165.71   $165.70   $165.70  
  Purchase #5 $222.46   6.140%   $236.119   $236.12   $236.10   $236.10  
  Purchase #6 $140.31   9.105%   $153.0852   $153.09   $153.10   $153.10  
  Purchase #7 $189.39   4.393%   $197.7099   $197.71   $197.70   $197.70  
  7 purchase totals = $1,038.00       $1,124.9742   $1,124.99   $1,124.95   $1,125.00