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 $123.89   10.205%   $136.533   $136.53   $136.55   $136.50  
  Purchase #2 $65.65   12.186%   $73.6501   $73.65   $73.65   $73.70  
  Purchase #3 $65.47   11.159%   $72.7758   $72.78   $72.80   $72.80  
  Purchase #4 $138.26   5.381%   $145.6998   $145.70   $145.70   $145.70  
  Purchase #5 $171.73   8.791%   $186.8268   $186.83   $186.85   $186.80  
  Purchase #6 $68.80   13.200%   $77.8816   $77.88   $77.90   $77.90  
  Purchase #7 $198.96   5.778%   $210.4559   $210.46   $210.45   $210.50  
  7 purchase totals = $832.76       $903.8230   $903.83   $903.90   $903.90