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 $89.83   12.697%   $101.2357   $101.24   $101.25   $101.20  
  Purchase #2 $63.69   11.492%   $71.0093   $71.01   $71.00   $71.00  
  Purchase #3 $123.55   3.457%   $127.8211   $127.82   $127.80   $127.80  
  Purchase #4 $223.35   7.243%   $239.5272   $239.53   $239.55   $239.50  
  Purchase #5 $42.73   8.519%   $46.3702   $46.37   $46.35   $46.40  
  Purchase #6 $8.99   6.352%   $9.561   $9.56   $9.55   $9.60  
  Purchase #7 $243.95   7.640%   $262.5878   $262.59   $262.60   $262.60  
  7 purchase totals = $796.09       $858.1123   $858.12   $858.10   $858.10