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 $55.91   12.560%   $62.9323   $62.93   $62.95   $62.90  
  Purchase #2 $54.50   3.487%   $56.4004   $56.40   $56.40   $56.40  
  Purchase #3 $201.67   13.357%   $228.6071   $228.61   $228.60   $228.60  
  Purchase #4 $76.94   9.226%   $84.0385   $84.04   $84.05   $84.00  
  Purchase #5 $239.73   4.502%   $250.5226   $250.52   $250.50   $250.50  
  Purchase #6 $234.72   6.865%   $250.8335   $250.83   $250.85   $250.80  
  Purchase #7 $76.73   8.207%   $83.0272   $83.03   $83.05   $83.00  
  7 purchase totals = $940.20       $1,016.3616   $1,016.36   $1,016.40   $1,016.20