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 $34.56   11.490%   $38.5309   $38.53   $38.55   $38.50  
  Purchase #2 $228.36   11.685%   $255.0439   $255.04   $255.05   $255.00  
  Purchase #3 $201.48   12.562%   $226.7899   $226.79   $226.80   $226.80  
  Purchase #4 $190.58   11.629%   $212.7425   $212.74   $212.75   $212.70  
  Purchase #5 $193.82   12.426%   $217.9041   $217.90   $217.90   $217.90  
  Purchase #6 $91.61   6.521%   $97.5839   $97.58   $97.60   $97.60  
  Purchase #7 $48.26   12.841%   $54.4571   $54.46   $54.45   $54.50  
  7 purchase totals = $988.67       $1,103.0523   $1,103.04   $1,103.10   $1,103.00