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 $153.46   13.816%   $174.662   $174.66   $174.65   $174.70  
  Purchase #2 $208.30   8.476%   $225.9555   $225.96   $225.95   $226.00  
  Purchase #3 $221.65   13.207%   $250.9233   $250.92   $250.90   $250.90  
  Purchase #4 $181.64   13.661%   $206.4538   $206.45   $206.45   $206.50  
  Purchase #5 $139.38   7.387%   $149.676   $149.68   $149.70   $149.70  
  Purchase #6 $81.62   3.485%   $84.4645   $84.46   $84.45   $84.50  
  Purchase #7 $76.42   9.748%   $83.8694   $83.87   $83.85   $83.90  
  7 purchase totals = $1,062.47       $1,176.0045   $1,176.00   $1,175.95   $1,176.20