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 $72.84   6.482%   $77.5615   $77.56   $77.55   $77.60  
  Purchase #2 $90.80   4.236%   $94.6463   $94.65   $94.65   $94.60  
  Purchase #3 $102.67   11.511%   $114.4883   $114.49   $114.50   $114.50  
  Purchase #4 $101.40   4.478%   $105.9407   $105.94   $105.95   $105.90  
  Purchase #5 $120.87   11.190%   $134.3954   $134.40   $134.40   $134.40  
  Purchase #6 $101.80   11.165%   $113.166   $113.17   $113.15   $113.20  
  Purchase #7 $201.92   10.688%   $223.5012   $223.50   $223.50   $223.50  
  7 purchase totals = $792.30       $863.6994   $863.71   $863.70   $863.70