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 $195.94   4.119%   $204.0108   $204.01   $204.00   $204.00  
  Purchase #2 $22.88   9.473%   $25.0474   $25.05   $25.05   $25.00  
  Purchase #3 $60.53   4.641%   $63.3392   $63.34   $63.35   $63.30  
  Purchase #4 $147.62   4.425%   $154.1522   $154.15   $154.15   $154.20  
  Purchase #5 $79.58   9.236%   $86.93   $86.93   $86.95   $86.90  
  Purchase #6 $159.83   11.269%   $177.8412   $177.84   $177.85   $177.80  
  Purchase #7 $63.86   4.676%   $66.8461   $66.85   $66.85   $66.80  
  7 purchase totals = $730.24       $778.1669   $778.17   $778.20   $778.00