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 $247.82   8.257%   $268.2825   $268.28   $268.30   $268.30  
  Purchase #2 $147.74   13.217%   $167.2668   $167.27   $167.25   $167.30  
  Purchase #3 $10.75   12.709%   $12.1162   $12.12   $12.10   $12.10  
  Purchase #4 $26.29   4.702%   $27.5262   $27.53   $27.55   $27.50  
  Purchase #5 $108.72   11.446%   $121.1641   $121.16   $121.15   $121.20  
  Purchase #6 $179.71   12.163%   $201.5681   $201.57   $201.55   $201.60  
  Purchase #7 $243.88   4.557%   $254.9936   $254.99   $255.00   $255.00  
  7 purchase totals = $964.91       $1,052.9175   $1,052.92   $1,052.90   $1,053.00