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 $195.40   5.831%   $206.7938   $206.79   $206.80   $206.80  
  Purchase #2 $105.91   11.859%   $118.4699   $118.47   $118.45   $118.50  
  Purchase #3 $80.89   8.442%   $87.7187   $87.72   $87.70   $87.70  
  Purchase #4 $153.76   7.280%   $164.9537   $164.95   $164.95   $165.00  
  Purchase #5 $220.60   11.745%   $246.5095   $246.51   $246.50   $246.50  
  Purchase #6 $193.49   4.266%   $201.7443   $201.74   $201.75   $201.70  
  Purchase #7 $33.79   8.170%   $36.5506   $36.55   $36.55   $36.60  
  7 purchase totals = $983.84       $1,062.7405   $1,062.73   $1,062.70   $1,062.80