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 $196.35   3.658%   $203.5325   $203.53   $203.55   $203.50  
  Purchase #2 $49.71   10.256%   $54.8083   $54.81   $54.80   $54.80  
  Purchase #3 $218.73   10.405%   $241.4889   $241.49   $241.50   $241.50  
  Purchase #4 $88.97   4.475%   $92.9514   $92.95   $92.95   $93.00  
  Purchase #5 $174.52   4.548%   $182.4572   $182.46   $182.45   $182.50  
  Purchase #6 $74.65   6.468%   $79.4784   $79.48   $79.50   $79.50  
  Purchase #7 $159.82   6.541%   $170.2738   $170.27   $170.25   $170.30  
  7 purchase totals = $962.75       $1,024.9905   $1,024.99   $1,025.00   $1,025.10