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 $58.93   8.440%   $63.9037   $63.90   $63.90   $63.90  
  Purchase #2 $196.43   11.632%   $219.2787   $219.28   $219.30   $219.30  
  Purchase #3 $105.65   13.429%   $119.8377   $119.84   $119.85   $119.80  
  Purchase #4 $132.51   12.145%   $148.6033   $148.60   $148.60   $148.60  
  Purchase #5 $212.45   3.217%   $219.2845   $219.28   $219.30   $219.30  
  Purchase #6 $37.79   9.711%   $41.4598   $41.46   $41.45   $41.50  
  Purchase #7 $108.64   4.402%   $113.4223   $113.42   $113.40   $113.40  
  7 purchase totals = $852.40       $925.7900   $925.78   $925.80   $925.80