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 $83.88   9.597%   $91.93   $91.93   $91.95   $91.90  
  Purchase #2 $94.71   4.263%   $98.7475   $98.75   $98.75   $98.70  
  Purchase #3 $49.85   12.441%   $56.0518   $56.05   $56.05   $56.10  
  Purchase #4 $133.70   11.133%   $148.5848   $148.58   $148.60   $148.60  
  Purchase #5 $153.48   12.260%   $172.2966   $172.30   $172.30   $172.30  
  Purchase #6 $125.97   7.177%   $135.0109   $135.01   $135.00   $135.00  
  Purchase #7 $66.49   10.526%   $73.4887   $73.49   $73.50   $73.50  
  7 purchase totals = $708.08       $776.1103   $776.11   $776.15   $776.10