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 $165.48   10.841%   $183.4197   $183.42   $183.40   $183.40  
  Purchase #2 $143.58   12.321%   $161.2705   $161.27   $161.25   $161.30  
  Purchase #3 $151.37   5.843%   $160.2145   $160.21   $160.20   $160.20  
  Purchase #4 $178.43   10.789%   $197.6808   $197.68   $197.70   $197.70  
  Purchase #5 $48.59   10.131%   $53.5127   $53.51   $53.50   $53.50  
  Purchase #6 $247.86   13.608%   $281.5888   $281.59   $281.60   $281.60  
  Purchase #7 $176.31   12.137%   $197.7087   $197.71   $197.70   $197.70  
  7 purchase totals = $1,111.62       $1,235.3957   $1,235.39   $1,235.35   $1,235.40