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 $195.30   10.592%   $215.9862   $215.99   $216.00   $216.00  
  Purchase #2 $228.88   11.255%   $254.6404   $254.64   $254.65   $254.60  
  Purchase #3 $58.29   3.457%   $60.3051   $60.31   $60.30   $60.30  
  Purchase #4 $79.77   5.684%   $84.3041   $84.30   $84.30   $84.30  
  Purchase #5 $220.40   9.298%   $240.8928   $240.89   $240.90   $240.90  
  Purchase #6 $221.85   6.512%   $236.2969   $236.30   $236.30   $236.30  
  Purchase #7 $33.28   4.686%   $34.8395   $34.84   $34.85   $34.80  
  7 purchase totals = $1,037.77       $1,127.2650   $1,127.27   $1,127.30   $1,127.20