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 $193.43   4.243%   $201.6372   $201.64   $201.65   $201.60  
  Purchase #2 $84.88   6.851%   $90.6951   $90.70   $90.70   $90.70  
  Purchase #3 $212.67   5.274%   $223.8862   $223.89   $223.90   $223.90  
  Purchase #4 $136.38   12.383%   $153.2679   $153.27   $153.25   $153.30  
  Purchase #5 $30.51   8.430%   $33.082   $33.08   $33.10   $33.10  
  Purchase #6 $225.99   11.831%   $252.7269   $252.73   $252.75   $252.70  
  Purchase #7 $94.34   9.496%   $103.2985   $103.30   $103.30   $103.30  
  7 purchase totals = $978.20       $1,058.5938   $1,058.61   $1,058.65   $1,058.60