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 $61.58   13.338%   $69.7935   $69.79   $69.80   $69.80  
  Purchase #2 $62.29   9.159%   $67.9951   $68.00   $68.00   $68.00  
  Purchase #3 $191.93   7.431%   $206.1923   $206.19   $206.20   $206.20  
  Purchase #4 $175.90   9.519%   $192.6439   $192.64   $192.65   $192.60  
  Purchase #5 $194.45   6.189%   $206.4845   $206.48   $206.50   $206.50  
  Purchase #6 $12.76   12.459%   $14.3498   $14.35   $14.35   $14.30  
  Purchase #7 $177.83   13.570%   $201.9615   $201.96   $201.95   $202.00  
  7 purchase totals = $876.74       $959.4206   $959.41   $959.45   $959.40