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 $240.47   10.609%   $265.9815   $265.98   $266.00   $266.00  
  Purchase #2 $94.41   10.872%   $104.6743   $104.67   $104.65   $104.70  
  Purchase #3 $41.94   7.331%   $45.0146   $45.01   $45.00   $45.00  
  Purchase #4 $86.68   12.579%   $97.5835   $97.58   $97.60   $97.60  
  Purchase #5 $23.53   8.115%   $25.4395   $25.44   $25.45   $25.40  
  Purchase #6 $180.50   6.768%   $192.7162   $192.72   $192.70   $192.70  
  Purchase #7 $112.35   7.557%   $120.8403   $120.84   $120.85   $120.80  
  7 purchase totals = $779.88       $852.2499   $852.24   $852.25   $852.20