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 $44.70   8.703%   $48.5902   $48.59   $48.60   $48.60  
  Purchase #2 $145.57   6.295%   $154.7336   $154.73   $154.75   $154.70  
  Purchase #3 $201.26   11.451%   $224.3063   $224.31   $224.30   $224.30  
  Purchase #4 $134.75   8.361%   $146.0164   $146.02   $146.00   $146.00  
  Purchase #5 $40.34   7.219%   $43.2521   $43.25   $43.25   $43.30  
  Purchase #6 $174.50   9.452%   $190.9937   $190.99   $191.00   $191.00  
  Purchase #7 $235.94   4.229%   $245.9179   $245.92   $245.90   $245.90  
  7 purchase totals = $977.06       $1,053.8102   $1,053.81   $1,053.80   $1,053.80