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 $86.49   7.106%   $92.636   $92.64   $92.65   $92.60  
  Purchase #2 $180.48   7.523%   $194.0575   $194.06   $194.05   $194.10  
  Purchase #3 $50.45   4.683%   $52.8126   $52.81   $52.80   $52.80  
  Purchase #4 $181.88   4.365%   $189.8191   $189.82   $189.80   $189.80  
  Purchase #5 $29.29   11.554%   $32.6742   $32.67   $32.65   $32.70  
  Purchase #6 $222.74   13.215%   $252.1751   $252.18   $252.20   $252.20  
  Purchase #7 $166.72   7.264%   $178.8305   $178.83   $178.85   $178.80  
  7 purchase totals = $918.05       $993.0050   $993.01   $993.00   $993.00