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 $202.38   7.847%   $218.2608   $218.26   $218.25   $218.30  
  Purchase #2 $96.36   6.342%   $102.4712   $102.47   $102.45   $102.50  
  Purchase #3 $82.83   5.503%   $87.3881   $87.39   $87.40   $87.40  
  Purchase #4 $245.50   6.690%   $261.924   $261.92   $261.90   $261.90  
  Purchase #5 $158.76   11.626%   $177.2174   $177.22   $177.20   $177.20  
  Purchase #6 $115.74   5.308%   $121.8835   $121.88   $121.90   $121.90  
  Purchase #7 $201.81   8.708%   $219.3836   $219.38   $219.40   $219.40  
  7 purchase totals = $1,103.38       $1,188.5286   $1,188.52   $1,188.50   $1,188.60