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 $183.60   5.821%   $194.2874   $194.29   $194.30   $194.30  
  Purchase #2 $129.95   6.419%   $138.2915   $138.29   $138.30   $138.30  
  Purchase #3 $78.45   4.643%   $82.0924   $82.09   $82.10   $82.10  
  Purchase #4 $111.47   6.599%   $118.8259   $118.83   $118.85   $118.80  
  Purchase #5 $20.36   10.403%   $22.4781   $22.48   $22.50   $22.50  
  Purchase #6 $173.43   6.510%   $184.7203   $184.72   $184.70   $184.70  
  Purchase #7 $7.92   12.772%   $8.9315   $8.93   $8.95   $8.90  
  7 purchase totals = $705.18       $749.6271   $749.63   $749.70   $749.60