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 $114.94   10.699%   $127.2374   $127.24   $127.25   $127.20  
  Purchase #2 $202.67   3.454%   $209.6702   $209.67   $209.65   $209.70  
  Purchase #3 $17.53   3.300%   $18.1085   $18.11   $18.10   $18.10  
  Purchase #4 $202.58   8.235%   $219.2625   $219.26   $219.25   $219.30  
  Purchase #5 $10.56   3.645%   $10.9449   $10.94   $10.95   $10.90  
  Purchase #6 $129.39   3.325%   $133.6922   $133.69   $133.70   $133.70  
  Purchase #7 $126.35   6.400%   $134.4364   $134.44   $134.45   $134.40  
  7 purchase totals = $804.02       $853.3521   $853.35   $853.35   $853.30