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 $54.72   5.391%   $57.67   $57.67   $57.65   $57.70  
  Purchase #2 $109.51   5.390%   $115.4126   $115.41   $115.40   $115.40  
  Purchase #3 $152.89   8.709%   $166.2052   $166.21   $166.20   $166.20  
  Purchase #4 $176.82   6.420%   $188.1718   $188.17   $188.15   $188.20  
  Purchase #5 $176.45   5.424%   $186.0206   $186.02   $186.00   $186.00  
  Purchase #6 $97.74   4.498%   $102.1363   $102.14   $102.15   $102.10  
  Purchase #7 $204.37   3.260%   $211.0325   $211.03   $211.05   $211.00  
  7 purchase totals = $972.50       $1,026.6490   $1,026.65   $1,026.60   $1,026.60