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 $161.35   13.418%   $182.9999   $183.00   $183.00   $183.00  
  Purchase #2 $62.91   7.530%   $67.6471   $67.65   $67.65   $67.60  
  Purchase #3 $201.93   7.786%   $217.6523   $217.65   $217.65   $217.70  
  Purchase #4 $136.33   11.742%   $152.3379   $152.34   $152.35   $152.30  
  Purchase #5 $88.79   12.637%   $100.0104   $100.01   $100.00   $100.00  
  Purchase #6 $163.99   6.385%   $174.4608   $174.46   $174.45   $174.50  
  Purchase #7 $127.67   10.298%   $140.8175   $140.82   $140.80   $140.80  
  7 purchase totals = $942.97       $1,035.9259   $1,035.93   $1,035.90   $1,035.90