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 $63.65   6.160%   $67.5708   $67.57   $67.55   $67.60  
  Purchase #2 $180.75   6.136%   $191.8408   $191.84   $191.85   $191.80  
  Purchase #3 $218.33   12.314%   $245.2152   $245.22   $245.20   $245.20  
  Purchase #4 $136.41   12.485%   $153.4408   $153.44   $153.45   $153.40  
  Purchase #5 $11.49   13.659%   $13.0594   $13.06   $13.05   $13.10  
  Purchase #6 $53.44   6.421%   $56.8714   $56.87   $56.85   $56.90  
  Purchase #7 $41.47   3.656%   $42.9861   $42.99   $43.00   $43.00  
  7 purchase totals = $705.54       $770.9845   $770.99   $770.95   $771.00