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 $223.28   8.166%   $241.513   $241.51   $241.50   $241.50  
  Purchase #2 $129.80   6.814%   $138.6446   $138.64   $138.65   $138.60  
  Purchase #3 $123.55   3.503%   $127.878   $127.88   $127.90   $127.90  
  Purchase #4 $187.62   11.643%   $209.4646   $209.46   $209.45   $209.50  
  Purchase #5 $34.25   6.635%   $36.5225   $36.52   $36.50   $36.50  
  Purchase #6 $47.51   4.850%   $49.8142   $49.81   $49.80   $49.80  
  Purchase #7 $185.71   11.584%   $207.2226   $207.22   $207.20   $207.20  
  7 purchase totals = $931.72       $1,011.0595   $1,011.04   $1,011.00   $1,011.00