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 $226.98   11.656%   $253.4368   $253.44   $253.45   $253.40  
  Purchase #2 $94.74   6.595%   $100.9881   $100.99   $101.00   $101.00  
  Purchase #3 $176.58   4.661%   $184.8104   $184.81   $184.80   $184.80  
  Purchase #4 $78.44   13.378%   $88.9337   $88.93   $88.95   $88.90  
  Purchase #5 $67.78   12.242%   $76.0776   $76.08   $76.10   $76.10  
  Purchase #6 $49.91   4.272%   $52.0422   $52.04   $52.05   $52.00  
  Purchase #7 $243.59   7.268%   $261.2941   $261.29   $261.30   $261.30  
  7 purchase totals = $938.02       $1,017.5829   $1,017.58   $1,017.65   $1,017.50