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 $65.61   3.665%   $68.0146   $68.01   $68.00   $68.00  
  Purchase #2 $250.81   12.309%   $281.6822   $281.68   $281.70   $281.70  
  Purchase #3 $195.57   4.704%   $204.7696   $204.77   $204.75   $204.80  
  Purchase #4 $36.91   5.468%   $38.9282   $38.93   $38.95   $38.90  
  Purchase #5 $238.84   12.317%   $268.2579   $268.26   $268.25   $268.30  
  Purchase #6 $184.40   7.633%   $198.4753   $198.48   $198.50   $198.50  
  Purchase #7 $202.87   12.613%   $228.458   $228.46   $228.45   $228.50  
  7 purchase totals = $1,175.01       $1,288.5858   $1,288.59   $1,288.60   $1,288.70