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 $36.87   12.675%   $41.5433   $41.54   $41.55   $41.50  
  Purchase #2 $65.86   10.656%   $72.878   $72.88   $72.90   $72.90  
  Purchase #3 $129.82   9.275%   $141.8608   $141.86   $141.85   $141.90  
  Purchase #4 $228.79   8.732%   $248.7679   $248.77   $248.75   $248.80  
  Purchase #5 $195.85   6.699%   $208.97   $208.97   $208.95   $209.00  
  Purchase #6 $102.60   12.444%   $115.3675   $115.37   $115.35   $115.40  
  Purchase #7 $202.47   5.635%   $213.8792   $213.88   $213.90   $213.90  
  7 purchase totals = $962.26       $1,043.2667   $1,043.27   $1,043.25   $1,043.40