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 $62.83   11.333%   $69.9505   $69.95   $69.95   $70.00  
  Purchase #2 $57.84   5.840%   $61.2179   $61.22   $61.20   $61.20  
  Purchase #3 $205.63   12.679%   $231.7018   $231.70   $231.70   $231.70  
  Purchase #4 $72.47   7.204%   $77.6907   $77.69   $77.70   $77.70  
  Purchase #5 $184.26   4.730%   $192.9755   $192.98   $193.00   $193.00  
  Purchase #6 $80.30   10.715%   $88.9041   $88.90   $88.90   $88.90  
  Purchase #7 $245.39   12.393%   $275.8012   $275.80   $275.80   $275.80  
  7 purchase totals = $908.72       $998.2417   $998.24   $998.25   $998.30