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 $182.76   11.360%   $203.5215   $203.52   $203.50   $203.50  
  Purchase #2 $6.85   12.195%   $7.6854   $7.69   $7.70   $7.70  
  Purchase #3 $183.58   5.539%   $193.7485   $193.75   $193.75   $193.70  
  Purchase #4 $168.65   11.222%   $187.5759   $187.58   $187.60   $187.60  
  Purchase #5 $59.77   13.452%   $67.8103   $67.81   $67.80   $67.80  
  Purchase #6 $228.68   10.805%   $253.3889   $253.39   $253.40   $253.40  
  Purchase #7 $15.68   7.489%   $16.8543   $16.85   $16.85   $16.90  
  7 purchase totals = $845.97       $930.5848   $930.59   $930.60   $930.60