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 $204.68   3.587%   $212.0219   $212.02   $212.00   $212.00  
  Purchase #2 $234.35   10.834%   $259.7395   $259.74   $259.75   $259.70  
  Purchase #3 $33.68   9.771%   $36.9709   $36.97   $36.95   $37.00  
  Purchase #4 $78.32   10.475%   $86.524   $86.52   $86.50   $86.50  
  Purchase #5 $15.62   13.752%   $17.7681   $17.77   $17.75   $17.80  
  Purchase #6 $29.54   3.338%   $30.526   $30.53   $30.55   $30.50  
  Purchase #7 $45.82   13.168%   $51.8536   $51.85   $51.85   $51.90  
  7 purchase totals = $642.01       $695.4040   $695.40   $695.35   $695.40