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 $95.26   8.342%   $103.2066   $103.21   $103.20   $103.20  
  Purchase #2 $120.87   4.300%   $126.0674   $126.07   $126.05   $126.10  
  Purchase #3 $137.26   12.862%   $154.9144   $154.91   $154.90   $154.90  
  Purchase #4 $219.57   4.655%   $229.791   $229.79   $229.80   $229.80  
  Purchase #5 $160.68   3.824%   $166.8244   $166.82   $166.80   $166.80  
  Purchase #6 $70.90   12.470%   $79.7412   $79.74   $79.75   $79.70  
  Purchase #7 $181.61   10.264%   $200.2505   $200.25   $200.25   $200.30  
  7 purchase totals = $986.15       $1,060.7955   $1,060.79   $1,060.75   $1,060.80