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 $211.84   4.216%   $220.7712   $220.77   $220.75   $220.80  
  Purchase #2 $242.98   7.435%   $261.0456   $261.05   $261.05   $261.00  
  Purchase #3 $5.81   3.717%   $6.026   $6.03   $6.05   $6.00  
  Purchase #4 $55.59   10.621%   $61.4942   $61.49   $61.50   $61.50  
  Purchase #5 $137.31   12.604%   $154.6166   $154.62   $154.60   $154.60  
  Purchase #6 $118.75   10.382%   $131.0786   $131.08   $131.10   $131.10  
  Purchase #7 $245.46   5.297%   $258.462   $258.46   $258.45   $258.50  
  7 purchase totals = $1,017.74       $1,093.4942   $1,093.50   $1,093.50   $1,093.50