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 $176.93   4.287%   $184.515   $184.52   $184.50   $184.50  
  Purchase #2 $107.32   12.518%   $120.7543   $120.75   $120.75   $120.80  
  Purchase #3 $72.66   11.630%   $81.1104   $81.11   $81.10   $81.10  
  Purchase #4 $169.77   6.846%   $181.3925   $181.39   $181.40   $181.40  
  Purchase #5 $89.36   5.146%   $93.9585   $93.96   $93.95   $94.00  
  Purchase #6 $156.59   11.493%   $174.5869   $174.59   $174.60   $174.60  
  Purchase #7 $123.95   3.864%   $128.7394   $128.74   $128.75   $128.70  
  7 purchase totals = $896.58       $965.0570   $965.06   $965.05   $965.10