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 $175.93   10.232%   $193.9312   $193.93   $193.95   $193.90  
  Purchase #2 $113.82   8.149%   $123.0952   $123.10   $123.10   $123.10  
  Purchase #3 $211.61   6.643%   $225.6673   $225.67   $225.65   $225.70  
  Purchase #4 $142.78   7.823%   $153.9497   $153.95   $153.95   $153.90  
  Purchase #5 $195.91   13.294%   $221.9543   $221.95   $221.95   $222.00  
  Purchase #6 $76.50   13.767%   $87.0318   $87.03   $87.05   $87.00  
  Purchase #7 $33.91   12.429%   $38.1247   $38.12   $38.10   $38.10  
  7 purchase totals = $950.46       $1,043.7542   $1,043.75   $1,043.75   $1,043.70