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 $192.92   6.376%   $205.2206   $205.22   $205.20   $205.20  
  Purchase #2 $140.25   11.543%   $156.4391   $156.44   $156.45   $156.40  
  Purchase #3 $49.67   13.794%   $56.5215   $56.52   $56.50   $56.50  
  Purchase #4 $87.37   7.326%   $93.7707   $93.77   $93.75   $93.80  
  Purchase #5 $97.56   9.291%   $106.6243   $106.62   $106.60   $106.60  
  Purchase #6 $246.66   13.663%   $280.3612   $280.36   $280.35   $280.40  
  Purchase #7 $55.76   3.135%   $57.5081   $57.51   $57.50   $57.50  
  7 purchase totals = $870.19       $956.4455   $956.44   $956.35   $956.40