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 $234.71   12.209%   $263.3657   $263.37   $263.35   $263.40  
  Purchase #2 $83.35   12.793%   $94.013   $94.01   $94.00   $94.00  
  Purchase #3 $81.55   4.331%   $85.0819   $85.08   $85.10   $85.10  
  Purchase #4 $219.46   3.266%   $226.6276   $226.63   $226.65   $226.60  
  Purchase #5 $120.75   11.277%   $134.367   $134.37   $134.35   $134.40  
  Purchase #6 $171.68   6.117%   $182.1817   $182.18   $182.20   $182.20  
  Purchase #7 $217.86   9.364%   $238.2604   $238.26   $238.25   $238.30  
  7 purchase totals = $1,129.36       $1,223.8973   $1,223.90   $1,223.90   $1,224.00