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 $50.90   3.789%   $52.8286   $52.83   $52.85   $52.80  
  Purchase #2 $212.61   7.153%   $227.818   $227.82   $227.80   $227.80  
  Purchase #3 $95.91   11.465%   $106.9061   $106.91   $106.90   $106.90  
  Purchase #4 $86.55   8.698%   $94.0781   $94.08   $94.10   $94.10  
  Purchase #5 $193.42   5.774%   $204.5881   $204.59   $204.60   $204.60  
  Purchase #6 $37.97   4.843%   $39.8089   $39.81   $39.80   $39.80  
  Purchase #7 $42.85   10.835%   $47.4928   $47.49   $47.50   $47.50  
  7 purchase totals = $720.21       $773.5206   $773.53   $773.55   $773.50