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 $202.60   13.737%   $230.4312   $230.43   $230.45   $230.40  
  Purchase #2 $174.81   13.512%   $198.4303   $198.43   $198.45   $198.40  
  Purchase #3 $221.92   6.140%   $235.5459   $235.55   $235.55   $235.50  
  Purchase #4 $45.81   11.735%   $51.1858   $51.19   $51.20   $51.20  
  Purchase #5 $175.52   11.313%   $195.3766   $195.38   $195.40   $195.40  
  Purchase #6 $166.75   11.304%   $185.5994   $185.60   $185.60   $185.60  
  Purchase #7 $248.51   7.351%   $266.778   $266.78   $266.80   $266.80  
  7 purchase totals = $1,235.92       $1,363.3472   $1,363.36   $1,363.45   $1,363.30