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 $147.70   11.826%   $165.167   $165.17   $165.15   $165.20  
  Purchase #2 $65.49   12.163%   $73.4555   $73.46   $73.45   $73.50  
  Purchase #3 $182.92   4.865%   $191.8191   $191.82   $191.80   $191.80  
  Purchase #4 $53.91   9.319%   $58.9339   $58.93   $58.95   $58.90  
  Purchase #5 $175.54   6.401%   $186.7763   $186.78   $186.80   $186.80  
  Purchase #6 $156.50   3.768%   $162.3969   $162.40   $162.40   $162.40  
  Purchase #7 $170.36   8.515%   $184.8662   $184.87   $184.85   $184.90  
  7 purchase totals = $952.42       $1,023.4149   $1,023.43   $1,023.40   $1,023.50