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 $168.27   10.642%   $186.1773   $186.18   $186.20   $186.20  
  Purchase #2 $33.72   9.391%   $36.8866   $36.89   $36.90   $36.90  
  Purchase #3 $16.74   9.301%   $18.297   $18.30   $18.30   $18.30  
  Purchase #4 $201.94   12.309%   $226.7968   $226.80   $226.80   $226.80  
  Purchase #5 $136.31   12.206%   $152.948   $152.95   $152.95   $152.90  
  Purchase #6 $114.30   10.343%   $126.122   $126.12   $126.10   $126.10  
  Purchase #7 $223.82   13.479%   $253.9887   $253.99   $254.00   $254.00  
  7 purchase totals = $895.10       $1,001.2164   $1,001.23   $1,001.25   $1,001.20