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 $216.76   3.407%   $224.145   $224.15   $224.15   $224.10  
  Purchase #2 $193.89   5.183%   $203.9393   $203.94   $203.95   $203.90  
  Purchase #3 $69.41   7.282%   $74.4644   $74.46   $74.45   $74.50  
  Purchase #4 $230.45   6.657%   $245.7911   $245.79   $245.80   $245.80  
  Purchase #5 $123.85   7.612%   $133.2775   $133.28   $133.30   $133.30  
  Purchase #6 $123.80   5.545%   $130.6647   $130.66   $130.65   $130.70  
  Purchase #7 $250.65   7.170%   $268.6216   $268.62   $268.60   $268.60  
  7 purchase totals = $1,208.81       $1,280.9036   $1,280.90   $1,280.90   $1,280.90