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 $202.32   13.722%   $230.0824   $230.08   $230.10   $230.10  
  Purchase #2 $223.92   13.592%   $254.3552   $254.36   $254.35   $254.40  
  Purchase #3 $239.25   8.625%   $259.8853   $259.89   $259.90   $259.90  
  Purchase #4 $33.44   12.410%   $37.5899   $37.59   $37.60   $37.60  
  Purchase #5 $114.28   9.758%   $125.4314   $125.43   $125.45   $125.40  
  Purchase #6 $60.89   11.229%   $67.7273   $67.73   $67.75   $67.70  
  Purchase #7 $70.60   4.834%   $74.0128   $74.01   $74.00   $74.00  
  7 purchase totals = $944.70       $1,049.0843   $1,049.09   $1,049.15   $1,049.10