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 $213.51   13.595%   $242.5367   $242.54   $242.55   $242.50  
  Purchase #2 $52.57   7.103%   $56.304   $56.30   $56.30   $56.30  
  Purchase #3 $109.66   7.342%   $117.7112   $117.71   $117.70   $117.70  
  Purchase #4 $235.89   8.663%   $256.3252   $256.33   $256.35   $256.30  
  Purchase #5 $35.70   11.111%   $39.6666   $39.67   $39.65   $39.70  
  Purchase #6 $161.72   9.817%   $177.5961   $177.60   $177.60   $177.60  
  Purchase #7 $113.77   9.437%   $124.5065   $124.51   $124.50   $124.50  
  7 purchase totals = $922.82       $1,014.6463   $1,014.66   $1,014.65   $1,014.60