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 $80.40   5.716%   $84.9957   $85.00   $85.00   $85.00  
  Purchase #2 $118.92   13.508%   $134.9837   $134.98   $135.00   $135.00  
  Purchase #3 $242.62   3.258%   $250.5246   $250.52   $250.50   $250.50  
  Purchase #4 $222.55   10.306%   $245.486   $245.49   $245.50   $245.50  
  Purchase #5 $60.33   3.149%   $62.2298   $62.23   $62.25   $62.20  
  Purchase #6 $136.76   11.178%   $152.047   $152.05   $152.05   $152.00  
  Purchase #7 $224.47   9.449%   $245.6802   $245.68   $245.70   $245.70  
  7 purchase totals = $1,086.05       $1,175.9470   $1,175.95   $1,176.00   $1,175.90