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 $81.98   11.745%   $91.6086   $91.61   $91.60   $91.60  
  Purchase #2 $55.41   12.144%   $62.139   $62.14   $62.15   $62.10  
  Purchase #3 $67.96   10.477%   $75.0802   $75.08   $75.10   $75.10  
  Purchase #4 $111.86   7.320%   $120.0482   $120.05   $120.05   $120.00  
  Purchase #5 $147.71   12.871%   $166.7218   $166.72   $166.70   $166.70  
  Purchase #6 $226.69   11.337%   $252.3898   $252.39   $252.40   $252.40  
  Purchase #7 $249.92   4.397%   $260.909   $260.91   $260.90   $260.90  
  7 purchase totals = $941.53       $1,028.8966   $1,028.90   $1,028.90   $1,028.80