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 $113.85   7.813%   $122.7451   $122.75   $122.75   $122.70  
  Purchase #2 $154.43   7.652%   $166.247   $166.25   $166.25   $166.20  
  Purchase #3 $66.72   11.238%   $74.218   $74.22   $74.20   $74.20  
  Purchase #4 $93.52   7.471%   $100.5069   $100.51   $100.50   $100.50  
  Purchase #5 $23.65   12.303%   $26.5597   $26.56   $26.55   $26.60  
  Purchase #6 $114.36   5.302%   $120.4234   $120.42   $120.40   $120.40  
  Purchase #7 $151.94   5.533%   $160.3468   $160.35   $160.35   $160.30  
  7 purchase totals = $718.47       $771.0469   $771.06   $771.00   $770.90