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 $92.36   11.459%   $102.9435   $102.94   $102.95   $102.90  
  Purchase #2 $59.70   6.511%   $63.5871   $63.59   $63.60   $63.60  
  Purchase #3 $34.41   10.245%   $37.9353   $37.94   $37.95   $37.90  
  Purchase #4 $72.79   3.301%   $75.1928   $75.19   $75.20   $75.20  
  Purchase #5 $17.69   11.707%   $19.761   $19.76   $19.75   $19.80  
  Purchase #6 $41.96   5.513%   $44.2733   $44.27   $44.25   $44.30  
  Purchase #7 $46.65   7.681%   $50.2332   $50.23   $50.25   $50.20  
  7 purchase totals = $365.56       $393.9262   $393.92   $393.95   $393.90