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 $111.72   13.848%   $127.191   $127.19   $127.20   $127.20  
  Purchase #2 $194.30   3.659%   $201.4094   $201.41   $201.40   $201.40  
  Purchase #3 $215.88   9.454%   $236.2893   $236.29   $236.30   $236.30  
  Purchase #4 $53.96   13.721%   $61.3639   $61.36   $61.35   $61.40  
  Purchase #5 $190.99   6.353%   $203.1236   $203.12   $203.10   $203.10  
  Purchase #6 $30.62   13.642%   $34.7972   $34.80   $34.80   $34.80  
  Purchase #7 $125.57   9.151%   $137.0609   $137.06   $137.05   $137.10  
  7 purchase totals = $923.04       $1,001.2353   $1,001.23   $1,001.20   $1,001.30