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 $83.29   11.663%   $93.0041   $93.00   $93.00   $93.00  
  Purchase #2 $139.67   11.866%   $156.2432   $156.24   $156.25   $156.20  
  Purchase #3 $229.76   8.810%   $250.0019   $250.00   $250.00   $250.00  
  Purchase #4 $235.40   8.693%   $255.8633   $255.86   $255.85   $255.90  
  Purchase #5 $44.98   9.333%   $49.178   $49.18   $49.20   $49.20  
  Purchase #6 $207.81   7.353%   $223.0903   $223.09   $223.10   $223.10  
  Purchase #7 $238.31   4.159%   $248.2213   $248.22   $248.20   $248.20  
  7 purchase totals = $1,179.22       $1,275.6021   $1,275.59   $1,275.60   $1,275.60