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 $52.36   13.529%   $59.4438   $59.44   $59.45   $59.40  
  Purchase #2 $247.28   11.125%   $274.7899   $274.79   $274.80   $274.80  
  Purchase #3 $219.48   8.784%   $238.7591   $238.76   $238.75   $238.80  
  Purchase #4 $169.86   7.600%   $182.7694   $182.77   $182.75   $182.80  
  Purchase #5 $31.98   5.447%   $33.722   $33.72   $33.70   $33.70  
  Purchase #6 $246.46   8.752%   $268.0302   $268.03   $268.05   $268.00  
  Purchase #7 $186.51   4.595%   $195.0801   $195.08   $195.10   $195.10  
  7 purchase totals = $1,153.93       $1,252.5945   $1,252.59   $1,252.60   $1,252.60