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 $203.53   5.149%   $214.0098   $214.01   $214.00   $214.00  
  Purchase #2 $178.86   4.834%   $187.5061   $187.51   $187.50   $187.50  
  Purchase #3 $91.80   11.405%   $102.2698   $102.27   $102.25   $102.30  
  Purchase #4 $233.76   10.780%   $258.9593   $258.96   $258.95   $259.00  
  Purchase #5 $162.52   8.169%   $175.7963   $175.80   $175.80   $175.80  
  Purchase #6 $53.41   8.683%   $58.0476   $58.05   $58.05   $58.00  
  Purchase #7 $220.38   11.819%   $246.4267   $246.43   $246.45   $246.40  
  7 purchase totals = $1,144.26       $1,243.0156   $1,243.03   $1,243.00   $1,243.00