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 $59.36   7.522%   $63.8251   $63.83   $63.85   $63.80  
  Purchase #2 $44.61   3.368%   $46.1125   $46.11   $46.10   $46.10  
  Purchase #3 $62.37   13.373%   $70.7107   $70.71   $70.70   $70.70  
  Purchase #4 $107.91   11.278%   $120.0801   $120.08   $120.10   $120.10  
  Purchase #5 $113.98   7.632%   $122.679   $122.68   $122.70   $122.70  
  Purchase #6 $43.48   7.755%   $46.8519   $46.85   $46.85   $46.90  
  Purchase #7 $127.66   11.479%   $142.3141   $142.31   $142.30   $142.30  
  7 purchase totals = $559.37       $612.5734   $612.57   $612.60   $612.60