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 $77.31   10.624%   $85.5234   $85.52   $85.50   $85.50  
  Purchase #2 $247.57   10.243%   $272.9286   $272.93   $272.95   $272.90  
  Purchase #3 $177.93   12.292%   $199.8012   $199.80   $199.80   $199.80  
  Purchase #4 $186.43   3.484%   $192.9252   $192.93   $192.95   $192.90  
  Purchase #5 $101.54   4.601%   $106.2119   $106.21   $106.20   $106.20  
  Purchase #6 $84.29   8.832%   $91.7345   $91.73   $91.75   $91.70  
  Purchase #7 $64.64   8.676%   $70.2482   $70.25   $70.25   $70.20  
  7 purchase totals = $939.71       $1,019.3730   $1,019.37   $1,019.40   $1,019.20