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 $176.41   6.414%   $187.7249   $187.72   $187.70   $187.70  
  Purchase #2 $24.39   5.239%   $25.6678   $25.67   $25.65   $25.70  
  Purchase #3 $45.37   8.662%   $49.2999   $49.30   $49.30   $49.30  
  Purchase #4 $160.28   7.662%   $172.5607   $172.56   $172.55   $172.60  
  Purchase #5 $81.81   3.865%   $84.972   $84.97   $84.95   $85.00  
  Purchase #6 $123.65   4.487%   $129.1982   $129.20   $129.20   $129.20  
  Purchase #7 $134.65   8.847%   $146.5625   $146.56   $146.55   $146.60  
  7 purchase totals = $746.56       $795.9860   $795.98   $795.90   $796.10