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 $192.25   12.752%   $216.7657   $216.77   $216.75   $216.80  
  Purchase #2 $167.58   10.238%   $184.7368   $184.74   $184.75   $184.70  
  Purchase #3 $59.73   9.151%   $65.1959   $65.20   $65.20   $65.20  
  Purchase #4 $246.99   12.210%   $277.1475   $277.15   $277.15   $277.10  
  Purchase #5 $46.57   13.623%   $52.9142   $52.91   $52.90   $52.90  
  Purchase #6 $56.29   4.176%   $58.6407   $58.64   $58.65   $58.60  
  Purchase #7 $164.62   7.735%   $177.3534   $177.35   $177.35   $177.40  
  7 purchase totals = $934.03       $1,032.7542   $1,032.76   $1,032.75   $1,032.70