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 $123.26   13.457%   $139.8471   $139.85   $139.85   $139.80  
  Purchase #2 $185.58   3.475%   $192.0289   $192.03   $192.05   $192.00  
  Purchase #3 $180.76   7.541%   $194.3911   $194.39   $194.40   $194.40  
  Purchase #4 $40.55   7.526%   $43.6018   $43.60   $43.60   $43.60  
  Purchase #5 $152.33   6.121%   $161.6541   $161.65   $161.65   $161.70  
  Purchase #6 $178.48   5.651%   $188.5659   $188.57   $188.55   $188.60  
  Purchase #7 $93.61   9.206%   $102.2277   $102.23   $102.25   $102.20  
  7 purchase totals = $954.57       $1,022.3166   $1,022.32   $1,022.35   $1,022.30