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 $194.28   4.787%   $203.5802   $203.58   $203.60   $203.60  
  Purchase #2 $228.66   8.450%   $247.9818   $247.98   $248.00   $248.00  
  Purchase #3 $105.58   4.298%   $110.1178   $110.12   $110.10   $110.10  
  Purchase #4 $191.89   13.349%   $217.5054   $217.51   $217.50   $217.50  
  Purchase #5 $94.97   11.538%   $105.9276   $105.93   $105.95   $105.90  
  Purchase #6 $213.46   13.291%   $241.831   $241.83   $241.85   $241.80  
  Purchase #7 $104.42   5.300%   $109.9543   $109.95   $109.95   $110.00  
  7 purchase totals = $1,133.26       $1,236.8981   $1,236.90   $1,236.95   $1,236.90