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 $181.95   12.477%   $204.6519   $204.65   $204.65   $204.70  
  Purchase #2 $111.82   12.310%   $125.585   $125.59   $125.60   $125.60  
  Purchase #3 $48.67   8.699%   $52.9038   $52.90   $52.90   $52.90  
  Purchase #4 $85.74   12.188%   $96.19   $96.19   $96.20   $96.20  
  Purchase #5 $113.97   8.399%   $123.5423   $123.54   $123.55   $123.50  
  Purchase #6 $163.66   9.583%   $179.3435   $179.34   $179.35   $179.30  
  Purchase #7 $20.33   5.345%   $21.4166   $21.42   $21.40   $21.40  
  7 purchase totals = $726.14       $803.6331   $803.63   $803.65   $803.60