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 $67.84   8.566%   $73.6512   $73.65   $73.65   $73.70  
  Purchase #2 $136.39   11.869%   $152.5781   $152.58   $152.60   $152.60  
  Purchase #3 $247.95   7.853%   $267.4215   $267.42   $267.40   $267.40  
  Purchase #4 $149.90   8.426%   $162.5306   $162.53   $162.55   $162.50  
  Purchase #5 $212.45   6.530%   $226.323   $226.32   $226.30   $226.30  
  Purchase #6 $52.34   6.512%   $55.7484   $55.75   $55.75   $55.70  
  Purchase #7 $128.68   8.493%   $139.6088   $139.61   $139.60   $139.60  
  7 purchase totals = $995.55       $1,077.8616   $1,077.86   $1,077.85   $1,077.80