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 $48.97   7.461%   $52.6237   $52.62   $52.60   $52.60  
  Purchase #2 $207.32   10.467%   $229.0202   $229.02   $229.00   $229.00  
  Purchase #3 $126.41   12.269%   $141.9192   $141.92   $141.90   $141.90  
  Purchase #4 $19.79   8.381%   $21.4486   $21.45   $21.45   $21.40  
  Purchase #5 $134.50   11.790%   $150.3576   $150.36   $150.35   $150.40  
  Purchase #6 $228.37   7.503%   $245.5046   $245.50   $245.50   $245.50  
  Purchase #7 $148.38   4.343%   $154.8241   $154.82   $154.80   $154.80  
  7 purchase totals = $913.74       $995.6980   $995.69   $995.60   $995.60