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 $152.92   6.181%   $162.372   $162.37   $162.35   $162.40  
  Purchase #2 $204.34   12.860%   $230.6181   $230.62   $230.60   $230.60  
  Purchase #3 $71.33   7.278%   $76.5214   $76.52   $76.50   $76.50  
  Purchase #4 $161.35   6.595%   $171.991   $171.99   $172.00   $172.00  
  Purchase #5 $69.93   6.653%   $74.5824   $74.58   $74.60   $74.60  
  Purchase #6 $250.65   10.147%   $276.0835   $276.08   $276.10   $276.10  
  Purchase #7 $111.64   7.868%   $120.4238   $120.42   $120.40   $120.40  
  7 purchase totals = $1,022.16       $1,112.5922   $1,112.58   $1,112.55   $1,112.60