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 $200.27   5.796%   $211.8776   $211.88   $211.90   $211.90  
  Purchase #2 $34.78   9.385%   $38.0441   $38.04   $38.05   $38.00  
  Purchase #3 $152.69   6.457%   $162.5492   $162.55   $162.55   $162.50  
  Purchase #4 $183.87   9.748%   $201.7936   $201.79   $201.80   $201.80  
  Purchase #5 $205.85   4.445%   $215   $215.00   $215.00   $215.00  
  Purchase #6 $7.94   7.341%   $8.5229   $8.52   $8.50   $8.50  
  Purchase #7 $17.94   4.331%   $18.717   $18.72   $18.70   $18.70  
  7 purchase totals = $803.34       $856.5044   $856.50   $856.50   $856.40