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 $238.61   10.245%   $263.0556   $263.06   $263.05   $263.10  
  Purchase #2 $153.43   11.288%   $170.7492   $170.75   $170.75   $170.70  
  Purchase #3 $39.68   8.510%   $43.0568   $43.06   $43.05   $43.10  
  Purchase #4 $5.54   7.569%   $5.9593   $5.96   $5.95   $6.00  
  Purchase #5 $206.71   4.710%   $216.446   $216.45   $216.45   $216.40  
  Purchase #6 $70.93   3.342%   $73.3005   $73.30   $73.30   $73.30  
  Purchase #7 $11.59   6.218%   $12.3107   $12.31   $12.30   $12.30  
  7 purchase totals = $726.49       $784.8781   $784.89   $784.85   $784.90