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 $163.83   12.647%   $184.5496   $184.55   $184.55   $184.50  
  Purchase #2 $220.89   6.682%   $235.6499   $235.65   $235.65   $235.60  
  Purchase #3 $188.77   5.767%   $199.6564   $199.66   $199.65   $199.70  
  Purchase #4 $249.69   11.218%   $277.7002   $277.70   $277.70   $277.70  
  Purchase #5 $108.55   12.803%   $122.4477   $122.45   $122.45   $122.40  
  Purchase #6 $39.80   5.474%   $41.9787   $41.98   $42.00   $42.00  
  Purchase #7 $146.60   6.440%   $156.041   $156.04   $156.05   $156.00  
  7 purchase totals = $1,118.13       $1,218.0235   $1,218.03   $1,218.05   $1,217.90