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 $200.68   10.147%   $221.043   $221.04   $221.05   $221.00  
  Purchase #2 $70.54   4.838%   $73.9527   $73.95   $73.95   $74.00  
  Purchase #3 $127.96   4.651%   $133.9114   $133.91   $133.90   $133.90  
  Purchase #4 $102.59   10.496%   $113.3578   $113.36   $113.35   $113.40  
  Purchase #5 $211.34   12.392%   $237.5293   $237.53   $237.55   $237.50  
  Purchase #6 $247.98   9.767%   $272.2002   $272.20   $272.20   $272.20  
  Purchase #7 $14.76   11.706%   $16.4878   $16.49   $16.50   $16.50  
  7 purchase totals = $975.85       $1,068.4822   $1,068.48   $1,068.50   $1,068.50