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 $238.81   5.830%   $252.7326   $252.73   $252.75   $252.70  
  Purchase #2 $186.66   9.865%   $205.074   $205.07   $205.05   $205.10  
  Purchase #3 $235.38   13.833%   $267.9401   $267.94   $267.95   $267.90  
  Purchase #4 $102.90   5.755%   $108.8219   $108.82   $108.80   $108.80  
  Purchase #5 $145.57   9.720%   $159.7194   $159.72   $159.70   $159.70  
  Purchase #6 $235.69   7.681%   $253.7933   $253.79   $253.80   $253.80  
  Purchase #7 $130.96   8.502%   $142.0942   $142.09   $142.10   $142.10  
  7 purchase totals = $1,275.97       $1,390.1755   $1,390.16   $1,390.15   $1,390.10