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 $232.59   11.279%   $258.8238   $258.82   $258.80   $258.80  
  Purchase #2 $138.25   5.347%   $145.6422   $145.64   $145.65   $145.60  
  Purchase #3 $221.34   12.807%   $249.687   $249.69   $249.70   $249.70  
  Purchase #4 $74.54   3.383%   $77.0617   $77.06   $77.05   $77.10  
  Purchase #5 $93.67   3.157%   $96.6272   $96.63   $96.65   $96.60  
  Purchase #6 $61.25   9.141%   $66.8489   $66.85   $66.85   $66.80  
  Purchase #7 $160.91   12.132%   $180.4316   $180.43   $180.45   $180.40  
  7 purchase totals = $982.55       $1,075.1224   $1,075.12   $1,075.15   $1,075.00