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 $91.76   4.391%   $95.7892   $95.79   $95.80   $95.80  
  Purchase #2 $163.94   11.642%   $183.0259   $183.03   $183.05   $183.00  
  Purchase #3 $62.56   11.444%   $69.7194   $69.72   $69.70   $69.70  
  Purchase #4 $87.47   13.854%   $99.5881   $99.59   $99.60   $99.60  
  Purchase #5 $163.36   8.758%   $177.6671   $177.67   $177.65   $177.70  
  Purchase #6 $48.71   4.670%   $50.9848   $50.98   $51.00   $51.00  
  Purchase #7 $164.34   12.613%   $185.0682   $185.07   $185.05   $185.10  
  7 purchase totals = $782.14       $861.8427   $861.85   $861.85   $861.90