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 $95.64   5.302%   $100.7108   $100.71   $100.70   $100.70  
  Purchase #2 $146.61   7.650%   $157.8257   $157.83   $157.85   $157.80  
  Purchase #3 $63.46   13.219%   $71.8488   $71.85   $71.85   $71.80  
  Purchase #4 $119.74   3.627%   $124.083   $124.08   $124.10   $124.10  
  Purchase #5 $174.32   8.819%   $189.6933   $189.69   $189.70   $189.70  
  Purchase #6 $120.25   3.294%   $124.211   $124.21   $124.20   $124.20  
  Purchase #7 $236.29   12.838%   $266.6249   $266.62   $266.60   $266.60  
  7 purchase totals = $956.31       $1,034.9975   $1,034.99   $1,035.00   $1,034.90