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 $54.70   7.784%   $58.9578   $58.96   $58.95   $59.00  
  Purchase #2 $58.83   7.649%   $63.3299   $63.33   $63.35   $63.30  
  Purchase #3 $127.90   3.851%   $132.8254   $132.83   $132.85   $132.80  
  Purchase #4 $185.91   9.455%   $203.4878   $203.49   $203.50   $203.50  
  Purchase #5 $42.70   4.458%   $44.6036   $44.60   $44.60   $44.60  
  Purchase #6 $160.45   11.695%   $179.2146   $179.21   $179.20   $179.20  
  Purchase #7 $185.82   7.635%   $200.0074   $200.01   $200.00   $200.00  
  7 purchase totals = $816.31       $882.4265   $882.43   $882.45   $882.40