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 $93.75   9.469%   $102.6272   $102.63   $102.65   $102.60  
  Purchase #2 $249.57   8.572%   $270.9631   $270.96   $270.95   $271.00  
  Purchase #3 $218.86   3.522%   $226.5682   $226.57   $226.55   $226.60  
  Purchase #4 $73.68   12.416%   $82.8281   $82.83   $82.85   $82.80  
  Purchase #5 $22.30   7.704%   $24.018   $24.02   $24.00   $24.00  
  Purchase #6 $99.62   6.728%   $106.3224   $106.32   $106.30   $106.30  
  Purchase #7 $134.69   10.155%   $148.3678   $148.37   $148.35   $148.40  
  7 purchase totals = $892.47       $961.6948   $961.70   $961.65   $961.70