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 $232.67   8.318%   $252.0235   $252.02   $252.00   $252.00  
  Purchase #2 $166.71   6.351%   $177.2978   $177.30   $177.30   $177.30  
  Purchase #3 $30.76   9.285%   $33.6161   $33.62   $33.60   $33.60  
  Purchase #4 $232.47   12.812%   $262.2541   $262.25   $262.25   $262.30  
  Purchase #5 $78.94   13.852%   $89.8748   $89.87   $89.85   $89.90  
  Purchase #6 $24.29   12.110%   $27.2315   $27.23   $27.25   $27.20  
  Purchase #7 $210.60   5.598%   $222.3894   $222.39   $222.40   $222.40  
  7 purchase totals = $976.44       $1,064.6872   $1,064.68   $1,064.65   $1,064.70