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 $81.66   13.690%   $92.8393   $92.84   $92.85   $92.80  
  Purchase #2 $160.90   10.231%   $177.3617   $177.36   $177.35   $177.40  
  Purchase #3 $84.45   7.821%   $91.0548   $91.05   $91.05   $91.10  
  Purchase #4 $184.49   11.820%   $206.2967   $206.30   $206.30   $206.30  
  Purchase #5 $30.49   10.385%   $33.6564   $33.66   $33.65   $33.70  
  Purchase #6 $172.32   11.721%   $192.5176   $192.52   $192.50   $192.50  
  Purchase #7 $177.58   12.469%   $199.7225   $199.72   $199.70   $199.70  
  7 purchase totals = $891.89       $993.4490   $993.45   $993.40   $993.50