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 $147.27   13.766%   $167.5432   $167.54   $167.55   $167.50  
  Purchase #2 $211.73   9.668%   $232.2001   $232.20   $232.20   $232.20  
  Purchase #3 $152.94   3.605%   $158.4535   $158.45   $158.45   $158.50  
  Purchase #4 $58.81   5.734%   $62.1822   $62.18   $62.20   $62.20  
  Purchase #5 $153.57   11.758%   $171.6268   $171.63   $171.65   $171.60  
  Purchase #6 $213.53   11.138%   $237.313   $237.31   $237.30   $237.30  
  Purchase #7 $191.54   5.151%   $201.4062   $201.41   $201.40   $201.40  
  7 purchase totals = $1,129.39       $1,230.7250   $1,230.72   $1,230.75   $1,230.70