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 $242.49   11.218%   $269.6925   $269.69   $269.70   $269.70  
  Purchase #2 $240.29   10.273%   $264.975   $264.98   $265.00   $265.00  
  Purchase #3 $219.34   8.477%   $237.9335   $237.93   $237.95   $237.90  
  Purchase #4 $132.97   12.847%   $150.0527   $150.05   $150.05   $150.10  
  Purchase #5 $89.50   5.337%   $94.2766   $94.28   $94.30   $94.30  
  Purchase #6 $208.85   9.222%   $228.1101   $228.11   $228.10   $228.10  
  Purchase #7 $21.62   5.290%   $22.7637   $22.76   $22.75   $22.80  
  7 purchase totals = $1,155.06       $1,267.8041   $1,267.80   $1,267.85   $1,267.90