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 $65.35   4.671%   $68.4025   $68.40   $68.40   $68.40  
  Purchase #2 $250.87   6.408%   $266.9457   $266.95   $266.95   $266.90  
  Purchase #3 $20.44   11.625%   $22.8162   $22.82   $22.80   $22.80  
  Purchase #4 $242.85   8.264%   $262.9191   $262.92   $262.90   $262.90  
  Purchase #5 $152.45   9.282%   $166.6004   $166.60   $166.60   $166.60  
  Purchase #6 $70.52   11.645%   $78.7321   $78.73   $78.75   $78.70  
  Purchase #7 $127.55   8.632%   $138.5601   $138.56   $138.55   $138.60  
  7 purchase totals = $930.03       $1,004.9761   $1,004.98   $1,004.95   $1,004.90