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 $191.32   11.690%   $213.6853   $213.69   $213.70   $213.70  
  Purchase #2 $245.42   6.215%   $260.6729   $260.67   $260.65   $260.70  
  Purchase #3 $119.37   13.764%   $135.8001   $135.80   $135.80   $135.80  
  Purchase #4 $167.89   10.560%   $185.6192   $185.62   $185.60   $185.60  
  Purchase #5 $83.81   9.381%   $91.6722   $91.67   $91.65   $91.70  
  Purchase #6 $193.48   11.701%   $216.1191   $216.12   $216.10   $216.10  
  Purchase #7 $147.49   11.258%   $164.0944   $164.09   $164.10   $164.10  
  7 purchase totals = $1,148.78       $1,267.6632   $1,267.66   $1,267.60   $1,267.70