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 $248.48   13.795%   $282.7578   $282.76   $282.75   $282.80  
  Purchase #2 $101.79   6.678%   $108.5875   $108.59   $108.60   $108.60  
  Purchase #3 $20.33   13.632%   $23.1014   $23.10   $23.10   $23.10  
  Purchase #4 $218.62   3.633%   $226.5625   $226.56   $226.55   $226.60  
  Purchase #5 $85.77   9.107%   $93.5811   $93.58   $93.60   $93.60  
  Purchase #6 $148.28   10.837%   $164.3491   $164.35   $164.35   $164.30  
  Purchase #7 $138.59   12.268%   $155.5922   $155.59   $155.60   $155.60  
  7 purchase totals = $961.86       $1,054.5316   $1,054.53   $1,054.55   $1,054.60