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 $215.74   8.772%   $234.6647   $234.66   $234.65   $234.70  
  Purchase #2 $136.95   11.725%   $153.0074   $153.01   $153.00   $153.00  
  Purchase #3 $132.83   12.803%   $149.8362   $149.84   $149.85   $149.80  
  Purchase #4 $235.79   4.703%   $246.8792   $246.88   $246.90   $246.90  
  Purchase #5 $26.54   13.212%   $30.0465   $30.05   $30.05   $30.00  
  Purchase #6 $77.78   12.842%   $87.7685   $87.77   $87.75   $87.80  
  Purchase #7 $107.90   12.807%   $121.7188   $121.72   $121.70   $121.70  
  7 purchase totals = $933.53       $1,023.9213   $1,023.93   $1,023.90   $1,023.90