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 $44.95   8.557%   $48.7964   $48.80   $48.80   $48.80  
  Purchase #2 $203.60   3.864%   $211.4671   $211.47   $211.45   $211.50  
  Purchase #3 $218.56   11.238%   $243.1218   $243.12   $243.10   $243.10  
  Purchase #4 $59.73   6.384%   $63.5432   $63.54   $63.55   $63.50  
  Purchase #5 $124.71   7.634%   $134.2304   $134.23   $134.25   $134.20  
  Purchase #6 $190.82   8.268%   $206.597   $206.60   $206.60   $206.60  
  Purchase #7 $87.70   5.694%   $92.6936   $92.69   $92.70   $92.70  
  7 purchase totals = $930.07       $1,000.4495   $1,000.45   $1,000.45   $1,000.40