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 $239.86   12.400%   $269.6026   $269.60   $269.60   $269.60  
  Purchase #2 $210.77   11.461%   $234.9263   $234.93   $234.95   $234.90  
  Purchase #3 $16.91   9.805%   $18.568   $18.57   $18.55   $18.60  
  Purchase #4 $62.56   5.557%   $66.0365   $66.04   $66.05   $66.00  
  Purchase #5 $22.57   5.513%   $23.8143   $23.81   $23.80   $23.80  
  Purchase #6 $216.46   10.305%   $238.7662   $238.77   $238.75   $238.80  
  Purchase #7 $106.64   10.305%   $117.6293   $117.63   $117.65   $117.60  
  7 purchase totals = $875.77       $969.3432   $969.35   $969.35   $969.30