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 $126.29   6.231%   $134.1591   $134.16   $134.15   $134.20  
  Purchase #2 $20.73   13.596%   $23.5485   $23.55   $23.55   $23.50  
  Purchase #3 $85.69   7.357%   $91.9942   $91.99   $92.00   $92.00  
  Purchase #4 $210.71   12.603%   $237.2658   $237.27   $237.25   $237.30  
  Purchase #5 $39.78   11.841%   $44.4903   $44.49   $44.50   $44.50  
  Purchase #6 $197.56   12.411%   $222.0792   $222.08   $222.10   $222.10  
  Purchase #7 $205.33   13.854%   $233.7764   $233.78   $233.80   $233.80  
  7 purchase totals = $886.09       $987.3135   $987.32   $987.35   $987.40