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 $54.56   13.193%   $61.7581   $61.76   $61.75   $61.80  
  Purchase #2 $151.61   10.673%   $167.7913   $167.79   $167.80   $167.80  
  Purchase #3 $193.91   9.355%   $212.0503   $212.05   $212.05   $212.10  
  Purchase #4 $56.31   13.528%   $63.9276   $63.93   $63.95   $63.90  
  Purchase #5 $49.71   11.489%   $55.4212   $55.42   $55.40   $55.40  
  Purchase #6 $180.55   7.487%   $194.0678   $194.07   $194.05   $194.10  
  Purchase #7 $241.84   4.304%   $252.2488   $252.25   $252.25   $252.20  
  7 purchase totals = $928.49       $1,007.2651   $1,007.27   $1,007.25   $1,007.30