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 $210.48   10.494%   $232.5678   $232.57   $232.55   $232.60  
  Purchase #2 $220.43   5.558%   $232.6815   $232.68   $232.70   $232.70  
  Purchase #3 $163.77   5.273%   $172.4056   $172.41   $172.40   $172.40  
  Purchase #4 $54.89   4.538%   $57.3809   $57.38   $57.40   $57.40  
  Purchase #5 $185.48   11.669%   $207.1237   $207.12   $207.10   $207.10  
  Purchase #6 $58.33   11.108%   $64.8093   $64.81   $64.80   $64.80  
  Purchase #7 $13.94   4.874%   $14.6194   $14.62   $14.60   $14.60  
  7 purchase totals = $907.32       $981.5882   $981.59   $981.55   $981.60