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 $33.94   6.573%   $36.1709   $36.17   $36.15   $36.20  
  Purchase #2 $128.33   13.400%   $145.5262   $145.53   $145.55   $145.50  
  Purchase #3 $113.99   8.149%   $123.279   $123.28   $123.30   $123.30  
  Purchase #4 $155.29   7.533%   $166.988   $166.99   $167.00   $167.00  
  Purchase #5 $105.94   3.107%   $109.2316   $109.23   $109.25   $109.20  
  Purchase #6 $190.44   13.830%   $216.7779   $216.78   $216.80   $216.80  
  Purchase #7 $24.75   7.491%   $26.604   $26.60   $26.60   $26.60  
  7 purchase totals = $752.68       $824.5776   $824.58   $824.65   $824.60