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 $43.87   11.836%   $49.0625   $49.06   $49.05   $49.10  
  Purchase #2 $118.45   5.475%   $124.9351   $124.94   $124.95   $124.90  
  Purchase #3 $238.48   3.184%   $246.0732   $246.07   $246.05   $246.10  
  Purchase #4 $209.92   11.747%   $234.5793   $234.58   $234.60   $234.60  
  Purchase #5 $175.76   4.554%   $183.7641   $183.76   $183.75   $183.80  
  Purchase #6 $241.78   6.631%   $257.8124   $257.81   $257.80   $257.80  
  Purchase #7 $210.29   4.799%   $220.3818   $220.38   $220.40   $220.40  
  7 purchase totals = $1,238.55       $1,316.6084   $1,316.60   $1,316.60   $1,316.70