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 $241.82   5.741%   $255.7029   $255.70   $255.70   $255.70  
  Purchase #2 $53.79   6.790%   $57.4423   $57.44   $57.45   $57.40  
  Purchase #3 $182.90   10.654%   $202.3862   $202.39   $202.40   $202.40  
  Purchase #4 $103.60   11.786%   $115.8103   $115.81   $115.80   $115.80  
  Purchase #5 $247.99   10.728%   $274.5944   $274.59   $274.60   $274.60  
  Purchase #6 $84.74   9.691%   $92.9522   $92.95   $92.95   $93.00  
  Purchase #7 $177.67   10.621%   $196.5403   $196.54   $196.55   $196.50  
  7 purchase totals = $1,092.51       $1,195.4286   $1,195.42   $1,195.45   $1,195.40