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 $62.74   5.607%   $66.2578   $66.26   $66.25   $66.30  
  Purchase #2 $162.52   7.752%   $175.1186   $175.12   $175.10   $175.10  
  Purchase #3 $229.94   9.576%   $251.9591   $251.96   $251.95   $252.00  
  Purchase #4 $218.59   12.368%   $245.6252   $245.63   $245.65   $245.60  
  Purchase #5 $61.41   10.429%   $67.8144   $67.81   $67.80   $67.80  
  Purchase #6 $50.27   13.298%   $56.9549   $56.95   $56.95   $57.00  
  Purchase #7 $41.35   5.611%   $43.6701   $43.67   $43.65   $43.70  
  7 purchase totals = $826.82       $907.4001   $907.40   $907.35   $907.50