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 $211.83   6.699%   $226.0205   $226.02   $226.00   $226.00  
  Purchase #2 $136.74   7.576%   $147.0994   $147.10   $147.10   $147.10  
  Purchase #3 $90.97   4.201%   $94.7916   $94.79   $94.80   $94.80  
  Purchase #4 $157.67   8.530%   $171.1193   $171.12   $171.10   $171.10  
  Purchase #5 $122.28   10.108%   $134.6401   $134.64   $134.65   $134.60  
  Purchase #6 $65.55   11.248%   $72.9231   $72.92   $72.90   $72.90  
  Purchase #7 $169.26   3.328%   $174.893   $174.89   $174.90   $174.90  
  7 purchase totals = $954.30       $1,021.4870   $1,021.48   $1,021.45   $1,021.40