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 $62.51   8.787%   $68.0028   $68.00   $68.00   $68.00  
  Purchase #2 $240.87   8.860%   $262.2111   $262.21   $262.20   $262.20  
  Purchase #3 $99.71   12.428%   $112.102   $112.10   $112.10   $112.10  
  Purchase #4 $110.67   7.859%   $119.3676   $119.37   $119.35   $119.40  
  Purchase #5 $115.35   13.744%   $131.2037   $131.20   $131.20   $131.20  
  Purchase #6 $220.74   3.392%   $228.2275   $228.23   $228.25   $228.20  
  Purchase #7 $76.44   11.767%   $85.4347   $85.43   $85.45   $85.40  
  7 purchase totals = $926.29       $1,006.5494   $1,006.54   $1,006.55   $1,006.50