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 $128.89   12.711%   $145.2732   $145.27   $145.25   $145.30  
  Purchase #2 $131.67   5.747%   $139.2371   $139.24   $139.25   $139.20  
  Purchase #3 $95.88   13.253%   $108.587   $108.59   $108.60   $108.60  
  Purchase #4 $239.81   9.363%   $262.2634   $262.26   $262.25   $262.30  
  Purchase #5 $114.79   9.584%   $125.7915   $125.79   $125.80   $125.80  
  Purchase #6 $60.53   3.664%   $62.7478   $62.75   $62.75   $62.70  
  Purchase #7 $190.60   10.692%   $210.979   $210.98   $211.00   $211.00  
  7 purchase totals = $962.17       $1,054.8790   $1,054.88   $1,054.90   $1,054.90