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 $111.42   12.131%   $124.9364   $124.94   $124.95   $124.90  
  Purchase #2 $161.85   10.295%   $178.5125   $178.51   $178.50   $178.50  
  Purchase #3 $10.94   5.774%   $11.5717   $11.57   $11.55   $11.60  
  Purchase #4 $205.53   11.186%   $228.5206   $228.52   $228.50   $228.50  
  Purchase #5 $49.51   4.152%   $51.5657   $51.57   $51.55   $51.60  
  Purchase #6 $232.99   3.464%   $241.0608   $241.06   $241.05   $241.10  
  Purchase #7 $190.45   11.272%   $211.9175   $211.92   $211.90   $211.90  
  7 purchase totals = $962.69       $1,048.0852   $1,048.09   $1,048.00   $1,048.10