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 $31.97   12.374%   $35.926   $35.93   $35.95   $35.90  
  Purchase #2 $111.45   10.531%   $123.1868   $123.19   $123.20   $123.20  
  Purchase #3 $183.67   5.188%   $193.1988   $193.20   $193.20   $193.20  
  Purchase #4 $96.67   3.454%   $100.009   $100.01   $100.00   $100.00  
  Purchase #5 $143.70   6.666%   $153.279   $153.28   $153.30   $153.30  
  Purchase #6 $11.46   9.180%   $12.512   $12.51   $12.50   $12.50  
  Purchase #7 $216.90   4.218%   $226.0488   $226.05   $226.05   $226.00  
  7 purchase totals = $795.82       $844.1604   $844.17   $844.20   $844.10